#include<bits/stdc++.h>
#define rep(i, n) for(int i = 0; i < n;++i)
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef pair<int, int> pii;
typedef array<int, 3> ai3;
const ll inf = 0x3f3f3f3f3f3f3f3fll;
const int Mod = 998244353;
const int inv2 = (Mod+1) / 2;
const int inv6 = (Mod+1) / 6;
inline int sign(int a){ return (a&1) ? (Mod-1) : 1; }
inline void uadd(int &a, int b){ a += b-Mod; a += (a>>31) & Mod; }
inline void usub(int &a, int b){ a -= b, a += (a>>31) & Mod; }
inline void umul(int &a, int b){ a = (int)(1ll * a * b % Mod); }
inline int add(int a, int b){ a += b-Mod; a += (a>>31) & Mod; return a; }
inline int sub(int a, int b){ a -= b, a += (a>>31) & Mod; return a; }
inline int mul(int a, int b){ a = (int)(1ll * a * b % Mod); return a; }
int qpow(int b, int p){ int ret = 1; while(p){ if(p&1) umul(ret, b); umul(b, b), p >>= 1; } return ret; }
const int fN = 100100;
int fact[fN], invfact[fN], pw2[fN], invpw2[fN];
void initfact(int n){
	pw2[0] = 1; for(int i = 1; i <= n; ++i) pw2[i] = mul(pw2[i-1], 2);
	invpw2[0] = 1; for(int i = 1; i <= n; ++i) invpw2[i] = mul(invpw2[i-1], (Mod+1) / 2);
	fact[0] = 1; for(int i = 1; i <= n; ++i) fact[i] = mul(fact[i-1], i);
	invfact[n] = qpow(fact[n], Mod-2); for(int i = n; i > 0; --i) invfact[i-1] = mul(invfact[i], i);
}
int binom(int n, int m){ return mul(fact[n], mul(invfact[m], invfact[n-m])); }
const double pi = acos(-1);
inline void chmax(ll &a, ll b){ (b>a) ? (a=b) : 0; }

int n, m;
const ull lmt = (1ull<<62) -1 ;
struct bigint{
	ull a[255];
	int len;
	bigint(int x = 0){ memset(a, 0, sizeof(a)), len = (bool)x, a[0] = x; }
} c[10010];

bigint operator +(bigint lh, bigint rh){
	bigint ret(0);
	ret.len = max(lh.len, rh.len);
	//rep(i, lh.len){ cout << lh.a[i] << " ";} cout << "+ "; rep(i, rh.len){ cout << rh.a[i] << " ";} cout << "= ";
	rep(i, ret.len) ret.a[i] += lh.a[i] + rh.a[i], ret.a[i+1] += ret.a[i] >> 62, ret.a[i] &= lmt;
	while(ret.a[ret.len]) ++ret.len;
	//rep(i, ret.len){ cout << ret.a[i] << " ";} cout << "\n";
	return ret;
}

bigint smallmul(bigint lh, int rh){
	bigint ret(0);
	if(!rh) return ret;
	ret.len = lh.len;
	ull car = 0;
	rep(i, ret.len + 1){
		__int128 cur = (__int128)lh.a[i] * rh + car;
		ret.a[i] = (ull)(cur & lmt);
		car = (ull)(cur >> 62);
	}
	while(ret.a[ret.len]) ++ret.len;
	return ret;
}

int a[10010];
vi rg[10010];
int deg[10010];

int main(){
	ios::sync_with_stdio(false);
	cin.tie(0);

	cin >> n >> m;
	rep(i, n) cin >> a[i];
	rep(i, m){
		int u, v;
		cin >> u >> v;
		--u, --v;
		++deg[u], rg[v].push_back(u);
	}

	queue<int> q;
	rep(i, n) if(!deg[i]) c[i] = bigint(1), q.push(i);
	while(!q.empty()){
		int u = q.front(); q.pop();
		rep(i, (int)rg[u].size()){
			int t = rg[u][i];
			c[t] = c[t] + c[u] + c[u];
			--deg[t];
			if(!deg[t]) q.push(t);
		}
	}

	bigint s = 0;
	rep(i, n) s = s + smallmul(c[i], a[i]);
	//rep(i, n){
	//	cout << i << ": ";
	//	for(int j = c[i].len-1; j >= 0; --j)
	//		cout << c[i].a[j] << " ";
	//	cout << "\n";
	//}
	int ans = 62 * (s.len - 1);
	//for(int j = s.len-1; j >= 0; --j){ cout << s.a[j] << " "; } cout << "\n";
	for(int i = 62; i >= 0; --i){
		if(s.a[s.len-1] >> i){
			ans += i+1;
			break;
		}
	}
	cout << ans << "\n";

	return 0;
}