#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define int long long
#define otto auto
const int MAXN=1e6+10;
const int INF=1ll*1e7*1e9;
int T,N,M,K,P,Q;
int a[MAXN];
int fa[MAXN];

int getfa(int x){
	if(fa[x] == x) return x;
	return fa[x] = getfa(fa[x]);
}

bool merge(int x,int y){
	x = getfa(x);
	y = getfa(y);
	if(x == y) return false;
	fa[y] = x;
	return true;
}

void prepare(){
	scanf("%lld %lld",&N,&M);
	for(int i = 1;i <= 2*N; i++){
		fa[i] = i;
	}
	for(int i = 1;i <= M; i++){
		int x,y;
		scanf("%lld %lld",&x,&y);
		if(!merge(x,y)){
			printf("2\n");
			return;
		}
	}
	printf("3\n");
}

signed main(){
	//ios::sync_with_stdio(0);
	T=1;
	//scanf("%lld",&T);
	while(T--){
	    prepare();
	}
	return 0;
}