#include<bits/stdc++.h>
const int N = 10
;
const int M = 45 + 1
;
bool vis[1
<< N][M];
int siz[1
<< N], link[N];
double f[1
<< N][M];
int main()
{
int
n, m;
scanf("%d%d"
, &n, &m);
int lim = 1
<< n;
for (int i = 0
, x, y; i < m; ++i) {
scanf("%d%d"
, &x, &y);
--x; --y;
link[x] |= (
1
<< y);
link[y] |= (
1
<< x);
}
for (int S = 1; S < lim; ++S) siz[S] = siz[S & (S - 1)] + 1
;
for (int S1 = 3; S1 < lim; ++S1) if (S1 & 1
) {
for (int S2 = (S1 - 1) & S1; S2 != 0; S2 = (S2 - 1) & S1) if (S2 & 1
) {
int T = 0
;
for (int i = 0; i < n; ++i) if ((S1 >> i) & (~S2 >> i) & 1
)
T += siz[link[i] & S2];
for (int i = 0
; i + T <= m; ++i)
f[S1][i] +=
1.0 / (i + T + 1
) - f[S2][i + T];
}
}
printf("%.6lf\n", f[lim - 1][0
]);
return 0
;}
