#include<bits/stdc++.h>
#define FOR(i,a,b) for(int i=a;i<=b;i++)
#define ROF(i,a,b) for(int i=a;i>=b;i--)
#define pb push_back
using namespace std;
inline int rd() {
	int r = 0; bool w = false; char ch = getchar();
	while( ch < '0' || ch > '9' ) w = !(ch^45), ch = getchar();
	while( ch >= '0' && ch <='9' ) r = (r<<1) + (r<<3) + (ch^48), ch = getchar();
	return w ? -r : r;
}

#define MAXN 100000
int n, m;
vector<int> to[MAXN+5];
int val[MAXN+5], dot[MAXN+5], lnum[MAXN+5], rnum[MAXN+5];
bool cmp_dot( int a , int b ) {
	return val[a] < val[b];
}
int a[MAXN+5];
int fa[MAXN+5], cnt, mincnt;
int find( int x ) {
	if( fa[x] == x ) return x;
	return fa[x] = find(fa[x]);
}
int main() {
	n = rd(), m = rd();
	FOR(i,1,n) val[i] = rd(), dot[i] = i;
	sort(dot+1, dot+1+n, cmp_dot);
	if( val[dot[1]] == val[dot[n]] ) {
		puts("-1");
		return 0;
	}
	FOR(i,1,m) {
		int u = rd(), v = rd();
		to[u].pb(v), to[v].pb(u);
	}
	FOR(i,1,n) fa[i] = i; cnt = 0, mincnt = 0;
	FOR(i,1,n) {
		while( val[cnt+1] == val[i] && cnt < n ) ++cnt;
		int u = dot[i];
		for(auto v: to[u]) if( val[v] <= val[u] ) {
			if( find(v) != find(u) ) {
				++mincnt;
				fa[find(v)] = find(u);
			}
		}
		lnum[i] = cnt - mincnt;
	}
	FOR(i,1,n) fa[i] = i; cnt = 0, mincnt = 0;
	ROF(i,n,1) {
		while( val[n-cnt] == val[i] && cnt < n ) ++cnt;
		int u = dot[i];
		for(auto v: to[u]) if( val[v] >= val[u] ) {
			if( find(v) != find(u) ) {
				++mincnt;
				fa[find(v)] = find(u);
			}
		}
		rnum[i] = cnt - mincnt;
	}
//	FOR(i,1,n) printf("%d ", lnum[i]); putchar('\n');
//	FOR(i,1,n) printf("%d ", rnum[i]); putchar('\n');
	int ans = -1;
	FOR(i,1,n-1) if( val[dot[i]] != val[dot[i-1]] ) {
		if( i - lnum[i] + 1 >= rnum[i+1] && (n-i) - rnum[i+1] + 1 >= lnum[i] ) {
			ans = val[dot[i]];
			break;
		}
	}
	printf("%d", ans);
	return 0;
}