#include <bits/stdc++.h>

#define ll long long
#define F first
#define S second
#define all(x) x.begin(), x.end()
#define pb push_back
#define FIO ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0)

using namespace std;

typedef pair <ll, ll> pii;

const ll N = 1e4 + 7, B = (1LL << 32);

struct BN {
	vector <ll> zn;
	void Cl() {
		ll vis = 0;
		for (ll& x : zn) {
			x += vis;
			vis = x/B;
			x = x%B;
		}
		if (vis) zn.pb(vis);
	}
	void Mul(ll a) {
		for (ll& x : zn) x *= a;
		Cl();
	}
} dp[N];

BN operator+(BN a, BN b) {
	if (a.zn.size() < b.zn.size()) swap(a, b);
	for (int i = 0; i < b.zn.size(); i++) a.zn[i] += b.zn[i];
	a.Cl();
	return a;
}

int n, m;
ll arr[N];
vector <int> adj[N];

BN DP(int x) {
	if (!dp[x].zn.empty()) return dp[x];
	for (auto it : adj[x]) dp[x] = dp[x] + DP(it);
	dp[x].Mul(2);
	return dp[x];
}

int main () {
//	FIO;
	cin >> n >> m;
	
	for (int i = 1; i <= n; i++) cin >> arr[i];
	for (int i = 0; i < m; i++) {
		int x, y;
		cin >> x >> y;
		adj[x].pb(y);
	}
	for (int i = 1; i <= n; i++) if (adj[i].empty()) dp[i].zn.pb(1);
	
	BN res;
	for (int i = 1; i <= n; i++) {
		BN x = DP(i);
		x.Mul(arr[i]);
		res = res + x;
	}
	
	int cnt = 0, x = res.zn.back();
	while (x) {
		cnt++;
		x /= 2;
	}
	cout << cnt + res.zn.size()-1;

	return 0;
}