#include <bits/stdc++.h>

using namespace std;

#define FOR(i,a,b) for (int i = (a); i <= (b); i++)
#define FORD(i,a,b) for (int i = (a); i >= (b); i--)
#define REP(i,b) for (int i = 0; i < (b); i++)

typedef pair<int, int> pii;

const int N = 2000;

int n;
pii d[N];

const int dx[4] = { 0, 0, -1, 1 };
const int dy[4] = { -1, 1, 0, 0 };

void gen() {
    n = 7;
    set<pii> exists;
    d[0] = make_pair(rand() % 10, rand() % 10);
    exists.insert(d[0]);
    FOR(i, 1, n-1) {
        while (true) {
            int j = rand() % i;
            int dir = rand() % 4;
            int nx = d[j].first + dx[dir];
            int ny = d[j].second + dy[dir];
            pii nxt = make_pair(nx, ny);
            if (exists.find(nxt) != exists.end()) continue;
            exists.insert(nxt);
            d[i] = nxt;
            break;
        }
    }
}

pair<int, int> slow() {
    int best_count = 0, best_mask = 0;
    REP(mask, 1 << n) {
        int count = 0;
        REP(i, n) if (mask & (1 << i)) {
            count++;     
            pii a = d[i];       
            REP(j, n) if (mask & (1 << j)) {
                pii b = d[j];
                if(abs(a.first - b.first) + abs(a.second - b.second) == 1) goto END;
            }
        }
        if (count > best_count) {
            best_count = count;
            best_mask = mask;
        }
        END:;
    }
    return make_pair(best_count, best_mask);
}

bool removed[N];
vector<int> siblings[N];
bool visited[N];

pii fast() {
    REP(i, n) {
        removed[i] = false;
        siblings[i].clear();
        visited[i] = false;
    }

    map<pii, int> ids;
    REP(i, n) ids[d[i]] = i;

    REP(i, n) if (!removed[i]) {
        REP(j, 4) {
            pii sib = make_pair(d[i].first + dx[j], d[i].second + dy[j]);
            if (ids.find(sib) != ids.end()) {
                siblings[i].push_back(ids[sib]);
            }
        }
    }

    int ans = 0;
    int ans_mask = 0;
    
    while (true) {
        REP(i, n) if (!removed[i]) {
            int count = 0;
            for (int s : siblings[i]) if (!removed[s]) count++;
            if (count == 0) {
                ans++;
                ans_mask |= 1 << i;
                removed[i] = true;
                goto next;
            } else if (count == 1) {
                ans++;
                ans_mask |= 1 << i;
                removed[i] = true;
                int ss = -1;
                for (int s : siblings[i]) if (!removed[s]) ss = s;
                removed[ss] = true;
                goto next;
            }
        }
        break;
        next:;
    }
    
    REP(ii, n) if (!removed[ii] && !visited[ii]) {
        queue<int> q;
        q.push(ii);
        visited[ii] = true;
        int a = 0, b = 0;
        int a_mask = 0, b_mask = 0;
        while (!q.empty()) {
            int v = q.front();
            q.pop();
            if ((d[v].first + d[v].second) % 2 == 0) {
                a++;
                a_mask |= 1 << v;
            } else {
                b++;
                b_mask |= 1 << v;
            }
            for (int s : siblings[v]) if (!removed[s] && !visited[s]) {
                visited[s] = true;
                q.push(s);
            }
        }
        
        if (a > b) {
            ans += a;
            ans_mask |= a_mask;
        } else {
            ans += b;
            ans_mask |= b_mask;
        }
    }
    
    return make_pair(ans, ans_mask);
}

void display(int best_mask) {
    int min_x = d[0].first, max_x = d[0].first;
    int min_y = d[0].second, max_y = d[0].second;
    map<pii, int> ids;
    REP(i, n) {
        ids[d[i]] = i;
        min_x = min(min_x, d[i].first);
        max_x = max(max_x, d[i].first);
        min_y = min(min_y, d[i].second);
        max_y = max(max_y, d[i].second);
    }
    FOR(x, min_x, max_x) {
        FOR(y, min_y, max_y) {
            pii xy = make_pair(x, y);
            if (ids.find(xy) != ids.end()) {
                int id = ids[xy];
                printf("%c", (best_mask & (1 << id)) ? '*' : '.');
            } else {
                printf(" ");
            }
        }
        printf("\n");
    }
    printf("\n");
    printf("\n");
}

int main() {
    srand(482);
    /*int count = 0;
    for (int tc = 0; ; tc++) {
        gen();
        pii ans = slow();
        pii actual = fast();
        if (ans.first != actual.first) {
            printf("\n");
            printf("=============================\n");
            printf("expected: %d\n", ans.first);
            printf("actual: %d\n", actual.first);
            display(ans.second);
            display(actual.second);
            count++;
            if (count >= 10) break;
        }
    }*/
    
    while (scanf("%d", &n) == 1) {
        REP(i, n) {
            int x, y;
            scanf("%d%d", &x, &y);
            d[i] = make_pair(x, y);
        }
        pii ans = fast();
        printf("%d\n", ans.first);
    }
    return 0;
}