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

const int N = 2e6 + 5;
typedef double db;

char s[N];

struct Node {
    db x, y;

    bool operator<(const Node &w) { return y < w.y; }
} w[N];

int main() {
    int n;
    db k;
    scanf("%d%lf", &n, &k);

    scanf("%s", s + 1);

    db sum = 0;
    w[0] = { 0, 0 };
    for (int i = 1; i <= n; i++) {
        sum += (s[i] - '0') - k;
        w[i] = { double(i), sum };
    }

    sort(w, w + n + 1);

    db ans = 2;

    for (int i = 1; i <= n; i++) {
        ans = min(ans, fabs((w[i].y - w[i - 1].y) / (w[i].x - w[i - 1].x)));
    }

    printf("%0.12lf\n", ans);
}