ABC_124 - C - Coloring Colorfully

#include <bits/stdc++.h>

#define SYNC ios::sync_with_stdio(0);
#define F first
#define S second
#define endl '\n'


using namespace std;

using ll = long long int;
using ii = pair<int, int>;
using vii = vector<ii>;
using vi = vector<int>;
using graph = vector<vi>;
const int INF = 0x3f3f3f3f;
const int MAXN = 58;
const ll mod = 1000000007;



int main() {
    SYNC
    string s;
    cin >> s;
    int ans = 0;
    for (int i = 1; i < s.size(); ++i) {
        if (s[i] == s[i-1]) {
            s[i] = !(s[i-1] - '0') + '0';
            ans ++;
        }
    }
    cout << ans << endl;
    return 0;
}