#include <bits/stdc++.h>
#include <atcoder/all>
#include <boost/multiprecision/cpp_dec_float.hpp>
#include <boost/multiprecision/cpp_int.hpp>
namespace mp = boost::multiprecision;
using Bint = mp::cpp_int;
using namespace std;
using namespace atcoder;
#define rep(i, n) for(int i=0;i<(n);++i)
#define rep1(i, n) for(int i=1;i<=(n);i++)
#define ll long long
using mint = modint998244353;
using P = pair<ll,ll>;
using lb = long double;
using T = tuple<ll, ll, ll>;
#ifdef LOCAL
#  include <debug_print.hpp>
#  define dbg(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#  define dbg(...) (static_cast<void>(0))
#endif

int main()
{
    int n;
    string s;
    cin >> n >> s;
    int ans = 0;
    int mx = 0;
    int sum = 0;
    vector<int> now(n);
    rep(i,n) {
        if(s[i]=='1') sum++;
        dbg(sum,mx);
        dbg(2*sum-i);
        if(2*sum-i<mx) {
            ans++;
            sum++;
        }
        now[i] = 2*sum-i;
        if(i>=1) mx = max(mx, now[i-1]);
    }
    cout << ans << endl;
    return 0;
}