#include <fstream>
using namespace std;

ifstream in("blis.in");
ofstream out("blis.out");

const int maxn = 100000;
int N, K, len, c;
bool sir[maxn];

int findmax()
{
    int max = 0, number;
    for (int i = 0; i < len; i++)
    {
        number = 0;
        for (int j = i; j < K+i && j < len; j++)
        {
            if (sir[j]) { number <<= 1; number += 1; }
            else number <<= 1;
            if (number > max) max = number;
        }
    }
    return max;
}

int main()
{
    in >> K; in.get();
    for (len = 0; !in.eof(); len++)
    {
        c = in.get() - 48;
        sir[len] = c;
    }
    out << findmax();

    return 0;
}