#include<bits/stdc++.h>
#define rep(i,a,b) for(int i=(a);i<=(b);++i)
#define per(i,a,b) for(int i=(a);i>=(b);--i)
#define SZ(x) ((int)(x).size())
#define pb push_back
#define eb emplace_back
using namespace std;
const int N=400005;
int n,m,b0[N],b1[N];
vector<int>e[N];
int dfn[N],low[N],st[N],top,idx;
int seq[N],len,bel[N],cnt;
void GG(){puts("impossible"),exit(0);}
void tarjan(int u,int fa){
	dfn[u]=low[u]=++idx,st[++top]=u;
	for(auto&x:e[u])if(x!=fa){
		if(!dfn[x])tarjan(x,u),low[u]=min(low[u],low[x]);
		else low[u]=min(low[u],dfn[x]);
	}
	if(dfn[u]==low[u]){
		++cnt;
		len=0;
		do{
			seq[++len]=st[top];
			bel[st[top]]=cnt;
		}while(st[top--]!=u);
		int cnt_e=0;
		rep(i,1,len)for(auto&x:e[seq[i]]){
			if(x<seq[i]){
				++cnt_e;
			}
		}
		if(len==1){
			if(b0[seq[1]]!=b1[seq[1]]){
				GG();
			}
		}else{
			vector<int>v1,v2;
			rep(i,1,len){
				v1.pb(b0[seq[i]]);
				v2.pb(b1[seq[i]]);
			}
			if(cnt_e==len){
				vector<int>v3(v2);
				v3.pop_back();
				v3.insert(v3.begin(),v2.back());
				vector<int>v4(v2);
				v4.erase(v4.begin());
				v4.pb(v2[0]);
				if(v2!=v1&&v3!=v1&&v4!=v1){
					GG();
				}
			}else{
				sort(v1.begin(),v1.end());
				sort(v2.begin(),v2.end());
				if(v1!=v2)GG();
			}
		}
	}
}
int main(){
#ifdef xay5421
	freopen("a.in","r",stdin);
#endif
	ios::sync_with_stdio(0),cin.tie(0);
	cin>>n>>m;
	rep(i,1,n){
		cin>>b0[i]>>b1[i];
	}
	rep(i,1,m){
		int u,v;
		cin>>u>>v;
		e[u].pb(v);
		e[v].pb(u);
	}
	rep(i,1,n)if(!dfn[i])tarjan(i,0);
	puts("possible");
	return 0;
}