#include <iostream>

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

    int result = 0;
    for (int i = 0; i < N; ++i) {
        if (S[i] == '0') {
            if (i > 0 && S[i - 1] == '0') {
                result++;
                S[i] = '1';
                continue;
            }
            if (i > 1 && S[i - 1] == '1' && S[i - 2] == '0') {
                result++;
                S[i] = '1';
            }
        }
    }

    std::cout << result << std::endl;

    return 0;
}