#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("O3,unroll-loops")
// #pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
// Ofast, O0, O1, O2, O3, unroll-loops, fast-math, trapv
typedef long long ll;
typedef pair<ll, ll> pll;
typedef pair<int, int> pii;
#define Mp make_pair
#define sep ' '
#define endl '\n'
#define F first
#define S second
#define pb push_back
#define all(x) (x).begin(),(x).end()
#define kill(res) cout << res << '\n', exit(0);
#define set_dec(x) cout << fixed << setprecision(x);
#define fast_io ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define file_io freopen("input.txt", "r", stdin) ; freopen("output.txt", "w", stdout);
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const ll N = 5e5 + 50;
const ll inf = 1e9 + 7;
ll n, dp[N][3][2], help[3][2], sz[N];
string s;
vector<int> adj[N];
void dfs(int v, int p = 0){
int x = s[v] - '0';
if(!x) sz[v]++;
for(int u: adj[v]){
if(u == p) continue;
dfs(u, v); sz[v] += sz[u];
}
if(!sz[v]) return;
dp[v][0][1-x] = dp[v][1][1-x] = dp[v][2][1-x] = 1;
for(int u: adj[v]){
if(u == p || !sz[u]) continue;
for(int i = 0; i < 3; i++) for(int j = 0; j < 2; j++) help[i][j] = inf;
for(int i = 0; i < 2; i++){
help[0][i] = min({dp[v][0][1-i] + dp[u][0][1] + 1, dp[v][0][i] + dp[u][0][0] + 3});
help[1][i] = min({dp[v][1][1-i] + dp[u][0][1] + 1, dp[v][1][i] + dp[u][0][0] + 3, dp[v][0][i] + dp[u][1][1], dp[v][0][1-i] + dp[u][1][0] + 2});
//help[2][i] = min({help[2][i], dp[v][1][i] + dp[u][1][1], dp[v][1][1-i] + dp[u][1][0] + 2});
//help[2][i] = min({help[2][i], dp[v][2][i] + dp[u][0][1], dp[v][2][1-i] + dp[u][0][0] + 2});
//help[2][i] = min({help[2][i], dp[v][0][i] + dp[u][2][1], dp[v][0][1-i] + dp[u][2][0] + 2});
help[2][i] = min({help[2][i], dp[v][1][i] + dp[u][1][1], dp[v][1][1-i] + dp[u][1][0] + 2});
help[2][i] = min({help[2][i], dp[v][2][1-i] + dp[u][0][1] + 1, dp[v][2][i] + dp[u][0][0] + 3});
help[2][i] = min({help[2][i], dp[v][0][1-i] + dp[u][2][1] + 3, dp[v][0][i] + dp[u][2][0] + 1});
}
for(int i = 0; i < 3; i++){
for(int j = 0; j < 2; j++){
dp[v][i][j] = help[i][j];
if(i) dp[v][i][j] = min(dp[v][i][j], dp[v][i-1][j]);
}
}
}
}
int main(){
fast_io;
cin >> n >> s;
s = "$" + s;
int u, v;
for(int i = 1; i < n; i++){
cin >> u >> v;
adj[u].pb(v);
adj[v].pb(u);
}
v = 1;
for(int i = n; i >= 1; i--) if(s[i] == '0') v = i;
for(int i = 1; i <= n; i++)
for(int j = 0; j < 3; j++)
for(int k = 0; k < 2; k++)
dp[i][j][k] = inf;
dfs(v);
cout << dp[v][2][1];
}
