#include <iostream>

int main(){
	int N, ans = 0;
	std::string S;
	std::cin >> N >> S;
	if(N > 1) if((S[0] | S[1]) == '0') S[1] = '1', ans ++;
	for(int n = 2; n < N; ++n){
		if(S[n] != '0') continue;
		if(S[n - 2] == '0'){
			S[n] = '1';
			ans ++;
		}
		if(S[n - 1] == '0'){
			S[n] = '1';
			ans ++;
		}
	}
	std::cout << ans << std::endl;
}