// #include <me>
#include <bits/stdc++.h>
using namespace std;
#define endl "\n"
#define pb push_back
#define int long long
const int N = 3e5 + 5, M = 1e9 + 7, LG = 20;
int n , u , v , A[N] , m;
void solve(){
cin >> n >> m;
int ans = 0 , cr = 0;
for (int i = 1 ; i <= n ; i++){
cin >> A[i];
cr = max(cr , 2 * A[i]);
}
for (int i = 1 ; i <= m ; i++){
cin >> u >> v;
}
cout << cr << endl;
}
signed main(){
ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
int ts = 1;
// cin >> ts;
while(ts--){
solve();
}
}
