#include<bits/stdc++.h>
#define ll long long
#define fi first
#define se second
#define pb push_back
using namespace std;
const int N=1e6+5;
const int P1=1333331;
const int P2=13333331;
const int mod=1e9+7;
int n,m,tot,pre[N],fa[N],now[N],low[N],dfn[N],pos[N],sz,num,edge[N],cnt;
ll f1[N],f2[N],h1[N],h2[N];
bool vs[N],flg[N],ban[N],ok;
vector<int>p,q;
vector<int>G[N],to[N],vec[N];
stack<int>stk;
pair<int,int>fk[N];
void add(int x,int y){
    to[x].pb(y);
    to[y].pb(x);
}
void tarjan(int u){
    dfn[u]=low[u]=++num,stk.push(u);
    for(auto v:G[u]){
        if(!dfn[v]){
            tarjan(v),low[u]=min(low[u],low[v]);
            if(low[v]>=dfn[u]){
                tot++;
                int tmp;
                do{
                    tmp=stk.top(),stk.pop();
                    vec[tot].pb(tmp);
                    add(tmp,tot),fa[tmp]=tot;
                }while(tmp!=v);
                vec[tot].pb(u);
                add(u,tot),fa[tot]=u;
                if(vec[tot].size()==2)ban[tot]=1;
            }
        }
        else low[u]=min(low[u],dfn[v]);
    }
}
ll get(int l,int r){
    ll x=(h1[r]-h1[l-1]*f1[r-l+1]%mod+mod)%mod,y=(h2[r]-h2[l-1]*f2[r-l+1]%mod+mod)%mod;
    return x*mod+y;
}
void dfs(int u){
    vs[u]=1;
    if(u<=n){
        p.pb(pre[u]);
        q.pb(now[u]);
    }
    else{
        if(!cnt)cnt=u;
        else ok=1;
        ok|=flg[u];
    }
    for(auto v:to[u]){
        if(vs[v]||ban[v])continue;
        dfs(v);
    }
}
int main(){
    //freopen("zoo.in","r",stdin);
    //freopen("zoo.out","w",stdout);
    ios::sync_with_stdio(false);
    cin.tie(0),cout.tie(0);
    cin>>n>>m,tot=n;
    f1[0]=1;for(int i=1;i<=n*2;i++)f1[i]=f1[i-1]*P1%mod;
    f2[0]=1;for(int i=1;i<=n*2;i++)f2[i]=f2[i-1]*P2%mod;
    for(int i=1;i<=n;i++)cin>>pre[i]>>now[i];
    for(int i=1;i<=m;i++){
        int u,v;cin>>u>>v;
        G[u].pb(v),G[v].pb(u);
        fk[i]={u,v};
    }
    for(int i=1;i<=n;i++){
        if(!dfn[i])tarjan(i);
    }
    for(int i=1;i<=m;i++){
        int u=fk[i].fi,v=fk[i].se;
        if(fa[u]==fa[v]||fa[fa[u]]==v)edge[fa[u]]++;
        else edge[fa[v]]++;
    }
    for(int i=n+1;i<=tot;i++){
        if(edge[i]>vec[i].size())flg[i]=1;
    }
    for(int i=1;i<=n;i++){
        if(!vs[i]){
            p.clear(),q.clear(),cnt=ok=0;
            dfs(i);
            if(ok||p.size()==1){
                sort(p.begin(),p.end());
                sort(q.begin(),q.end());
                for(int j=0;j<p.size();j++){
                    if(p[j]!=q[j]){
                        cout<<"impossible";
                        return 0;
                    }
                }
            }
            else{
                //cout<<cnt<<"\n";
                sz=0;for(auto e:vec[cnt])pos[++sz]=e;
                for(int j=1;j<=sz;j++)pos[sz+j]=pos[j];
                ll sm1=0,sm2=0;
                for(int j=1;j<=sz;j++){
                    sm1=(sm1*P1+now[pos[j]])%mod;
                    sm2=(sm2*P2+now[pos[j]])%mod;
                }
                ll sm=sm1*mod+sm2;
                for(int j=1;j<=sz*2;j++){
                    h1[j]=(h1[j-1]*P1+pre[pos[j]])%mod;
                    h2[j]=(h2[j-1]*P2+pre[pos[j]])%mod;
                }
                bool o=0;
                for(int j=1;j<=sz;j++){
                    if(get(j,j+sz-1)==sm)o=1;
                }
                if(!o){
                    cout<<"impossible";
                    return 0;
                }
            }
        }
    }
    cout<<"possible";
}