#include <bits/stdc++.h>   using namespace std;   long long n, m;   long long x[105];   double f[105][105525];   double sum[105525];   inline void read() {     cin >> n >> m;     for (long long i = 0; i <= n - 1; i++) {       cin >> x[i];     }   }   inline void solve() {     long long ms = n * m;     if (m == 1) {       puts( 1 );       return;     }     f[0][0] = 1;     for (long long i = 0; i <= n - 1; i++) {       for (long long s = 0; s <= ms; s++) {         if (s) {           sum[s] = sum[s - 1] + f[i][s];         } else {           sum[s] = f[i][s];         }         if (s > m) {           f[i + 1][s] = sum[s - 1] - sum[s - m - 1];         } else {           f[i + 1][s] = sum[s - 1];         }         if (s >= x[i]) {           f[i + 1][s] -= f[i][s - x[i]];         }         f[i + 1][s] /= (m - 1);       }     }     long long score = 0;     for (long long i = 0; i <= n - 1; i++) {       score += x[i];     }     double prob = 0;     for (long long s = 0; s <= score - 1; s++) {       prob += f[n][s];     }     prob *= (m - 1);     prob += 1.0;     cout.precision(20);     cout << fixed << prob;   }   int main() {     ios_base::sync_with_stdio(false);     cin.tie();     read();     solve();     return 0;   }   