#include<bits/stdc++.h> using namespace std; #define int long long #define double long double #define lson (pos<<1) #define rson (pos<<1|1) int read(){int x=0,f=1;char c=getchar();while(c>'9'||c<'0'){if(c=='-')f=-1;c=getchar();}while('0'<=c&&c<='9')x=x*10+c-'0',c=getchar();return x*f;} const int MAXN=5010,MAXM=5010,inf=1000000000; int n,m,q,mx,a[MAXN],p[MAXM],b[MAXN]; double f[MAXN][MAXM]; void slv(){ n=read(),m=read(); for(int i=1;i<=n;i++)a[i]=read(),p[a[i]]++,mx=max(mx,a[i]); for(int i=1;i<=m;i++)p[i]+=p[i-1]; double tmp=1; for(int i=0;i<=n;i++)for(int j=0;j<=m;j++)f[i][j]=-inf; f[0][0]=0; for(int i=1;i<=n;i++){ for(int o=0;o<=mx;o++){ for(int j=m;j>=o;j--){ f[i][j]=max(f[i][j],f[i-1][j-o]+tmp*p[o]/(n-i+1)); } } tmp*=(double)1.0*(n-i)/(n-i+1); } printf("%.10Lf",n-f[n][m]); } signed main(){ slv(); return 0; }