#include <iostream>
#include <string>
using namespace std;

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

    int operations = 0;  
    int count_0 = 0;     
    for (int i = 0; i < N; ++i) {
        if (S[i] == '0') {
            count_0++;  
        } else {
            if (count_0 > 0) {
                operations += count_0 - 1; 
            }
            count_0 = 0;  
        }
    }

    if (count_0 > 0) {
        operations += count_0 - 1;
    }

    cout << operations << endl;
}