#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;

int op(int a,int b){
    return min(a,b);
}
int e(){
    return 1e9;
}
int mapping(int a,int b){
    return a + b;
}
int composition(int a,int b){
    return a + b;
}
int id(){
    return 0;
}
int n,ans;
string s;
int main(){
	cin >> n >> s;
    vector<int> sum(n + 1,0);
    for(int i = 0; i < n; i++){
        sum[i + 1] = sum[i] + 2 * (s[i] - '0') - 1;
    }
    lazy_segtree<int,op,e,int,mapping,composition,id> seg(sum);
    for(int i = n; i >= 2; i--){
        int mi = seg.prod(0,i - 1);
        if(seg.get(i) < mi){
            ans++;
            seg.apply(i, n + 1, 2);
        }
    }
    cout << ans << endl;
}