#include <bits/stdc++.h>
using namespace std;
#define ll long long
int main()
{
    int n; cin >> n;
    string binary; cin >> binary;
    int ending =n-1;
    int start = 0;
    while(binary[ending] == '1' && ending >= 0) ending--;
    while(binary[start] == '0' && start < n) start++;
    int zeros = 0;
    for(int i = start; i <= ending; i++)
    {
        if(binary[i] == '0') zeros++;
    }
    if(ending < start) {
        cout << 0 << "\n" << 0;
        return 0;
    }
    else{
        cout << min(ending - start + 1 - zeros, zeros) << "\n";
    }

	return 0;
}