#include <bits/stdc++.h>

using namespace std;

#define ll long long
#define FOR(i, j, k, in) for (int i=j; i<k; i+=in)
#define RFOR(i, j, k, in) for (int i=j; i>=k; i-=in)
#define REP(i, j) FOR(i, 0, j, 1)
#define RREP(i, j) FOR(i, j, 0, 1)
#define ALL(a) a.begin(), a.end()
#define RALL(a) a.end(), a.begin()
#define F first
#define S second
#define PB push_back
#define MP make_pair
#define pii pair<int, int>
#define MOD 1000000007

void solve() {
    string s; cin >> s;
    char curr = ' ';
    int count = 0;
    REP(i, s.size() / 2) {
        if (curr != s[2*i]) {
            count++;
        }
        curr = s[2*i];
    }
    cout << count/2 << endl;
}

signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    ll n=1;
    //  cin >> n;
    REP(i, n) {
        solve();
    }
    return 0;
}