#include <iostream>
#include <string>
#include <cmath>
#include<algorithm>
#include<stack>
#include<queue>
#include<map>
#include<set>
#include<iomanip>
#define _USE_MATH_DEFINES
#include <math.h>
#include <functional>
#include<complex>
using namespace std;

#define rep(i,x) for(ll i=0;i<x;i++)
#define repn(i,x) for(ll i=1;i<=x;i++)

typedef long long ll;
const ll INF = 1e17;
const ll MOD = 1000000007;
const ll MAX = 4000001;
const double eps = 1E-18;

ll max(ll a, ll b) {
	if (a > b) { return a; }
	return b;
}

ll min(ll a, ll b) {
	if (a > b) { return b; }
	return a;
}

ll gcd(ll a, ll b) {
	if (b == 0) { return a; }
	if (a < b) { return gcd(b, a); }
	return gcd(b, a % b);
}

ll lcm(ll a, ll b) {
	return a / gcd(a, b) * b;
}

struct edge {
	ll ind;
	ll fr;
	ll to;
	ll d;
};

class mint {
	long long x;
public:
	mint(long long x = 0) : x((x% MOD + MOD) % MOD) {}
	mint operator-() const {
		return mint(-x);
	}
	mint& operator+=(const mint& a) {
		if ((x += a.x) >= MOD) x -= MOD;
		return *this;
	}
	mint& operator-=(const mint& a) {
		if ((x += MOD - a.x) >= MOD) x -= MOD;
		return *this;
	}
	mint& operator*=(const  mint& a) {
		(x *= a.x) %= MOD;
		return *this;
	}
	mint operator+(const mint& a) const {
		mint res(*this);
		return res += a;
	}
	mint operator-(const mint& a) const {
		mint res(*this);
		return res -= a;
	}
	mint operator*(const mint& a) const {
		mint res(*this);
		return res *= a;
	}

	mint pow(ll t) const {
		if (!t) return 1;
		mint a = pow(t >> 1);
		a *= a;
		if (t & 1) a *= *this;
		return a;
	}

	// for prime MOD
	mint inv() const {
		return pow(MOD - 2);
	}
	mint& operator/=(const mint& a) {
		return (*this) *= a.inv();
	}
	mint operator/(const mint& a) const {
		mint res(*this);
		return res /= a;
	}

	friend ostream& operator<<(ostream& os, const mint& m) {
		os << m.x;
		return os;
	}
};

mint pw(mint a, ll b) {
	if (b == 0) { return 1; }
	mint ret = pw(a, b >> 1);
	ret *= ret;
	if (b & 1) { ret *= a; }
	return ret;
}

typedef vector<ll> vll;
typedef vector<vector<ll>> vvll;
typedef vector<vector<vector<ll>>> vvvll;

typedef vector<mint> vmint;
typedef vector<vector<mint>> vvmint;
typedef vector<vector<vector<mint>>> vvvmint;

//////////////////////////////////////
ll N;
vll A;
vvll g;

vvll mn;
vll dp1;
vll dp2;

vll merge(vll a, vll b) {
	//rep(i, a.size())cout << a[i] << " ";
	//cout << endl;
	//rep(i, b.size())cout << b[i] << " ";
	//cout << endl;

	vll c(a.size() + b.size() - 1, INF);
	rep(i, a.size())rep(j, b.size()) {
		c[i + j] = min(c[i + j], a[i] + b[j]);
	}
	return c;
}

void dfs(ll u, ll v) {
	mn[v].assign(1, A[v]);

	for (ll w : g[v]) {
		if (u == w) { continue; }
		dfs(v, w);

		vll b(mn[w].size() + 1, INF);
		rep(i, mn[w].size()+1) {
			if(i<mn[w].size())b[i] = mn[w][i];
			if (i >= dp1[w] + 1) { b[i] = min(0, b[i]); }
		}
		mn[v]=merge(mn[v], b);
	}

	if (A[v] < 0) { dp1[v] = INF; }
	else {
		dp1[v] = 0;
		for (ll w : g[v]) {
			if (u == w) { continue; }
			dp1[v] += min(dp1[w], dp2[w] + 1);
		}
	}

	dp2[v] = INF;
	rep(i, mn[v].size()) {
		if (mn[v][i] < 0) { dp2[v] = i; break; }
	}

	//cout << v << " " << dp1[v] << " " << dp2[v] << endl;
	//for (ll x : mn[v]) { cout << x << " "; }
	//cout << endl;

	return;
}

int main() {
	cin >> N;
	A.assign(N + 1, 0);
	repn(i, N)cin >> A[i];

	g.resize(N + 1);
	repn(i, N-1) {
		ll u, v;
		cin >> u >> v;
		g[u].push_back(v);
		g[v].push_back(u);
	}

	mn.resize(N + 1);
	dp1.resize(N + 1);
	dp2.resize(N + 1);

	dfs(0, 1);

	cout << min(dp1[1], dp2[1]) << endl;

}



Measured memory_bytes: 126528