String problem

#include <bits/stdc++.h>
#define f(i,a,b) for(int i = (a); i <= (b); i++)

typedef long long ll;
using namespace std;

const int MAX = 2000005;
int A[MAX], L[MAX], R[MAX], S[MAX], N, K;

int main()
{
    string str;
    cin >> K >> str;
    N = str.length();
    f(i,1,N) A[i] = str[i-1] - '0';
    f(i,1,N) S[i] = S[i-1] + A[i];
    f(i,1,MAX-1) L[i] = MAX;
    f(i,1,N) L[S[i]] = min(L[S[i]], i);
    f(i,1,N) R[S[i]] = max(R[S[i]], i);
    ll ans = 0;
    f(i,0,N-1) ans += max(R[S[i]+K] - max(L[S[i]+K],i+1) + 1, 0);
    cout << ans;
}