#include<set>
#include<map>
#include<queue>
#include<stack>
#include<cmath>
#include<string>
#include<vector>
#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#define INF 1000000001
#define MOD 1000000007
#define ll long long
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1
#define pi acos(-1.0)
using namespace std;
const int MAXN = 105;
int n,m,a[12];
double c[MAXN],tp[MAXN];
int fx(int x)
{
    int ret = 1;
    for(int i = 1; i <= x; i++){
        ret *= i;
    }
    return ret;
}
int main()
{
    while(~scanf("%d%d",&n,&m)){
        for(int i = 1; i <= n; i++){
            scanf("%d",&a[i]);
        }
        memset(c,0,sizeof(c));
        memset(tp,0,sizeof(tp));
        for(int i = 0; i <= a[1]; i++){
            c[i] = 1.0 / fx(i);
        }
        for(int i = 2; i <= n; i++){
            for(int j = 0; j <= m; j++){
                for(int k = 0; k + j <= m && k <= a[i]; k ++){
                    tp[j + k] += c[j] * 1.0 / fx(k);
                }
            }
            for(int j = 0; j <= m; j++){
                c[j] = tp[j];
                tp[j] = 0;
            }
        }
        printf("%.0lf\n",c[m] * fx(m));
    }
    return 0;
}