ZOJ 3687

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;
typedef long long LL;
const LL MOD=55566677;
bool visr[55],visc[55];
bool cant[55][55];
int ban[30][2];
LL f[55];
LL ans;
int n,m;

void initial(){
	f[0]=1;
	for(LL i=1;i<55;i++)
	f[i]=(f[i-1]*i)%MOD;
}

void dfs(int i,int num){    //禁止位置公式求法，实在是妙极地运用了DFS啊，只好
								//学习一下了 
	if(i>=m){
		if(num&1) ans=((ans-f[n-num])%MOD+MOD)%MOD;
		else ans=(ans+f[n-num])%MOD;
		return ;
	}
	dfs(i+1,num);
	if(!visr[ban[i][0]]&&!visc[ban[i][1]]){
		visr[ban[i][0]]=visc[ban[i][1]]=true;
		dfs(i+1,num+1);
		visr[ban[i][0]]=visc[ban[i][1]]=false;
	}
}

int main(){
	initial();
	while(scanf("%d%d",&n,&m)!=EOF){
		memset(visc,false,sizeof(visc));
		memset(visr,false,sizeof(visr));
		memset(cant,false,sizeof(cant));
		for(int i=0;i<m;i++){
			scanf("%d%d",&ban[i][0],&ban[i][1]);
			if(cant[ban[i][0]][ban[i][1]]){
				i--;
				m--;
			}
			else
			cant[ban[i][0]][ban[i][1]]=true;
		}
		ans=0;
		dfs(0,0);
		printf("%lld\n",ans);
	}
	return 0;
}