#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>
#include <cmath>
typedef long long ll;
using namespace std;
int n,m;
int maps[25][25];
bool Isok[(1<<18)+100];
int dp[(1<<18)+100];
bool check(int S){
for(int i=1;i<=n;i++){
if(S&(1<<(i-1))){
for(int j=1;j<=n;j++){
if(j==i) continue;
if(S&(1<<(j-1))){
if(maps[i][j]==1) return false;
}
}
}
}
return true;
}
void init(){
for(int i=0;i<(1<<n);i++){
if(check(i)) Isok[i]=true;
}
}
int main(){
scanf("%d%d",&n,&m);
for(int i=1;i<=m;i++){
int u,v;scanf("%d%d",&u,&v);
maps[u][v]=1;maps[v][u]=1;
}
init();
memset(dp,0x3f,sizeof(dp));
dp[0]=0;
//cout<<" sss"<<endl;
for(int S=0;S<(1<<n);S++){
for(int S0=S;S0>0;S0=(S0-1)&S){
if(Isok[S0]) dp[S]=min(dp[S],dp[S^S0]+1);
}
}
printf("%d\n",dp[(1<<n)-1]-1);
return 0;
}