#include<bits/stdc++.h>
using namespace std;
#define int long long
const int N=1e6+10;

signed main()
{
	int t=1;
	//cin>>t;
	while(t--)
	{
		int n;
		cin>>n;
	 string s;
	 cin>>s;
	 int ans=0;
	 for(int i=0;i<s.length();i++)ans=ans+(s[i]=='0');
	 cout<<ans<<'\n';
	}
}