#include<bits/stdc++.h>
#define N 300005
using namespace std;
int n,m,ty[N],rt[N][2],f[N][2],ans=1e9;
queue<pair<int,int>>q;
vector<int>vec[N][2];
void jb(int u,int v){vec[v][ty[u]].push_back(u);rt[u][ty[v]]++;}
int main(){
	scanf("%d%d",&n,&m);
	for(int i=1;i<=n;i++) scanf("%d",&ty[i]);
	for(int u,v,i=1;i<=m;i++){
		scanf("%d%d",&u,&v);
		jb(u,v),jb(v,u);
	}
	for(int i=1;i<=n;i++)for(int j=0;j<2;j++)if(!rt[i][j]) q.push(make_pair(i,j));
	for(int o=1;o<=2*n;o++){
		if(q.empty()) return puts("infinity"),0;
		auto [u,p]=q.front();q.pop();
		for(int x:vec[u][p^1])
			if(--rt[x][ty[u]]==0) f[x][ty[u]]=f[u][p]+1,q.push(make_pair(x,ty[u]));
	}
	for(int x=0;x<2;x++)
		for(int y=0;y<2;y++){
			int mx=-1;
			for(int i=1;i<=n;i++)if(ty[i]^x) mx=max(mx,f[i][y]);
			ans=min(ans,mx);
		}
	printf("%d",ans+2);
}