给跪了

再给也跪了

//minamoto#include
    
     #define rint register int#define ll long longusing namespace std;#define getc() (p1==p2&&(p2=(p1=buf)+fread(buf,1,1<<21,stdin),p1==p2)?EOF:*p1++)char buf[1<<21],*p1=buf,*p2=buf;int read(){    int res,f=1;char ch;    while((ch=getc())>'9'||ch<'0')(ch=='-')&&(f=-1);    for(res=ch-'0';(ch=getc())>='0'&&ch<='9';res=res*10+ch-'0');    return res*f;}ll dp[2][65][2205],sz[2205];bool vis[2205];int n,m,up,mp[25][25];ll c[60][60];double res;int main(){//  freopen("testdata.in","r",stdin);    n=read(),m=read(),up=pow(2,n)-1;    for(rint i=1,u,v;i<=m;++i)u=read(),v=read(),mp[u-1][v-1]=mp[v-1][u-1]=1;    for(rint i=1;i<=up;++i)for(rint p1=1;p1
     
      >p1)&1)&&((i>>p2)&1)&&mp[p1][p2];//  for(rint i=0;i<=m+1;++i)c[i][0]=c[i][i]=1;//  for(rint i=1;i<=m+1;++i)for(rint j=1;j
      
       >p1)&1)==0)++p1;        for(rint k=(j-1)&j;k;k=(k-1)&j){            if(((k>>p1)&1)==0)continue;            for(rint rk=0;rk<=i;++rk)            dp[0][i][j]+=dp[1][rk][k]*c[i-rk][sz[j^k]];        }        dp[1][i][j]=c[i][sz[j]]-dp[0][i][j];    }    for(rint i=0;i<=m;++i)res+=1.0*dp[0][i][up]/c[i][m];    printf("%.6lf\n",res/(m+1));return 0;}