#include<bits/stdc++.h>
using namespace std;
namespace ac{
	const int MAXN = 1000005, inf = 0x7fffffff / 2;
	int n, m, k, u, v, t[MAXN], d1, d2;
	int head[MAXN], cnt;
	char ch[MAXN];
	struct node{
		int next, to;
	}ed[4 * MAXN];
	void add_edge(int u, int v){
		ed[++cnt].next = head[u];
		ed[cnt].to = v;
		head[u] = cnt;
	}
	int main(){
		bool flag = 1;
		scanf("%d%d%d", &n, &m, &k);
		for(int i = 1;i <= n;i++) scanf("%d", &t[i]);
		for(int i = 1;i <= m;i++){
			scanf("%d%d", &u, &v);
			add_edge(u, v);
			add_edge(v, u);
			if(u == 1 || v == 1) d1++;
			if(u == n || v == n) d2++;
			if(u == 1 && v == n || u == n && v == 1) flag = 0;
		}for(int _ = 0;_ < n;_++) ch[_] = '.';
		if(n == 2 && k == 1){
			printf("impossible");
			return 0;
		}
		if(!flag){
			if(k >= 2){
				k -= 2;
				ch[0] = ch[n - 1] = 'U';
			} else ch[0] = ch[n - 1] = 'P';
			for(int i = 0;i < n;i++){
				if(ch[i] == '.'){
					if(k){
						ch[i] = 'U'; 
						k--;
					} else ch[i] = 'P';
				} 
			}
		}else{
			ch[0] = 'U';
			k--;
			for(int i = head[1];i && k;i = ed[i].next){
				int v = ed[i].to;
				ch[v - 1] = 'U';
			}for(int i = 0;i < n;i++) if(ch[i] == '.') ch[i] = 'P';
		}printf("%s", ch);
		return 0;
	}
} int main(){
//	freopen("data.in", "r", stdin);
////	freopen("ex_data2.in", "r", stdin);
//	freopen("data.out", "w", stdout);
	return ac::main();
}//6MB