#include <bits/stdc++.h>
using namespace std;

int main() {
    int N;
    string S;
    cin >> N >> S;

    int operations = 0;
    int zeroCount = 0;

    for (int i = 0; i < N; ++i) {
        if (S[i] == '0') {
            zeroCount++;
        } else {
            if (zeroCount > 0) {
                operations += max(0, zeroCount - 1);
                zeroCount = 0;
            }
        }
    }

    if (zeroCount > 0) {
        operations += max(0, zeroCount - 1);
    }

    cout << operations << endl;
    return 0;
}