#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef vector<ll> vll;
typedef vector<vll> vvll;
#define REP(i, n) for(ll i = 0; i < n; ++i)
#define REPs(i, x, n) for(ll i = x; i < n; ++i)
#define endli "\n"
#define ll int

int main(){
    multiset<pair<ll, ll> > vision;
    ll n;
    cin >> n;
    ll a, b;
    ll sum = 0;
    for(ll i=0; i < n; i++){
    cin >> a >> b;
        if(a==b) continue;
        vision.insert({a, b});
        if(vision.count({b, a}) < 1){
            sum += 1;
        }
        else sum--;
    }

    cout << sum << endli;
    return 0;
}