求条B4153玄关

#include <bits/stdc++.h>
using namespace std;
int n,sum,ans,cnt,num[20000020];
string a;
int main()
{
	cin >> n >> a;
	num[n] = 1;
	for (int i = 0;i < n;i++)
	{
		if (a[i] == '1')
		{
			cnt += num[n + sum];
			sum++;
		}
		else
		{
			cnt -= num[n + sum - 1];
			sum--;
		}
		num[n + sum]++;
		ans += cnt;
	}
	cout << ans;
	return 0;
}