// Problem: B. 【NOIP Round #3】抓内鬼
// Contest: Public Judge - Public NOIP Round #3 (Div. 1, 提高)
// URL: https://pjudge.ac/contest/1030/problem/21694
// Memory Limit: 1024 MB
// Time Limit: 3000 ms
// 
// Powered by CP Editor (https://cpeditor.org)

#include<bits/stdc++.h>
#define int long long 
#define rep(i,a,b)	for(int i = (a);i<=(b);i++)
#define lep(i,a,b)	for(int i = (a);i>=(b);i--)
using namespace std;
const int N = 2e5+10;
int n,m,k,flag,u,v;
int t[N];
signed main(){
	ios::sync_with_stdio(false);
	cin.tie(0),cout.tie(0);
	cin>>n>>m>>k;
	if(k == 1){
		rep(i,1,n)	cin>>t[i];
		rep(i,1,m){
			cin>>u>>v;
			if(u>v)	swap(u,v);
			if(u == 1 && v == n)	flag = 1;
		}
		if(flag && n<=2)	cout<<"impossible";
		else{
			if(!flag){
				cout<<'U';
				rep(i,1,n-1)	cout<<'P';
			}
			else{
				cout<<"PU";
				rep(i,1,n-2)	cout<<'P';
			}
		}
	}
	else{
		rep(i,1,n)	cin>>t[i];
		rep(i,1,m){
			cin>>u>>v;
			if(u>v)	swap(u,v);
			if(u == 1 && v == n)	flag = 1;
		}
		if(flag && n<=2 && k == 1)	cout<<"impossible";
		else{
			if(!flag){
				cout<<'P';
				rep(i,1,n-k-1)	cout<<'P';
				rep(i,1,k)	cout<<'U';
			}
			else{
				if(n<=2){
					if(!k)	cout<<"PP";
					else cout<<"UU";
				}
				else{
					cout<<'P';
					rep(i,1,n-k-2)	cout<<'P';
					rep(i,1,k)	cout<<'U';
					cout<<'P';
				}
			}
		}
	}
	return 0;	
}