#include <bits/extc++.h>
#define rep(i, n) for (int i = 0; i < (n); ++i)

using namespace std;

int main() {
    int n;
    string s;
    cin >> n >> s;
    
    int ans = 0;
    rep(i, n) if (s[i] == '0') {
        int l = i;
        while (i < n and s[i] == '0') ++i;
        int r = i;
        ans += r-l-1;
    }
    
    cout << ans << '\n';
    
    return 0;
}