#include <bits/stdc++.h>
using namespace std;

#define rep(i, n) for (int i = 0; i < (int)(n); i++)

int main()
{
    long long N, A;
    cin >> N >> A;

    string S;
    cin >> S;

    int zero_cnt = 0;
    vector<vector<long long>> AC_counts(2, vector<long long>(N));

    rep(i, 2) rep(j, N)
    {
        if (S[j] == '0')
        {
            zero_cnt++;
        }
        if (S[j] == '1' && 0 < zero_cnt)
        {
            zero_cnt--;
            AC_counts[i][j]++;
        }
    }

    rep(i, N - 1)
    {
        AC_counts[0][i + 1] += AC_counts[0][i];
        AC_counts[1][i + 1] += AC_counts[1][i];
    }

    long long ans = 0;
    if (A <= AC_counts[0].back())
    {
        ans = distance(AC_counts[0].begin(), find(AC_counts[0].begin(), AC_counts[0].end(), A)) + 1;
    }
    else
    {
        A -= AC_counts[0].back();

        long long cycle = (A + AC_counts[1].back() - 1) / AC_counts[1].back() - 1;
        ans += N + cycle * N;
        A -= cycle * AC_counts[1].back();
        ans += distance(AC_counts[1].begin(), find(AC_counts[1].begin(), AC_counts[1].end(), A)) + 1;
    }

    cout << ans << endl;

    return 0;
}