#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N = 5e5 + 7;
const int INF = 1e9 + 7;
int n, dp[N][2][3], nxtDp[2][3], cnt[N];
string s;
vector<int> adj[N];
void Dfs(int u, int p){
int state = s[u] - '0';
cnt[u] = (state == 0);
for(int v : adj[u]){
if (v == p)
continue;
Dfs(v, u);
cnt[u] += cnt[v];
}
if (cnt[u] == 0)
return;
dp[u][state ^ 1][0] = 1;
dp[u][state ^ 1][1] = 1;
dp[u][state ^ 1][2] = 1;
for(int v : adj[u]){
if (v == p || cnt[v] == 0)
continue;
memset(nxtDp, 0x3f, sizeof(nxtDp));
for(int s = 0; s < 2; s++){
nxtDp[s][0] = min(nxtDp[s][0], dp[u][s ^ 1][0] + dp[v][1][0] + 1);
nxtDp[s][0] = min(nxtDp[s][0], dp[u][s][0] + dp[v][0][0] + 3);
nxtDp[s][1] = min(nxtDp[s][1], dp[u][s ^ 1][1] + dp[v][1][0] + 1);
nxtDp[s][1] = min(nxtDp[s][1], dp[u][s][1] + dp[v][0][0] + 3);
nxtDp[s][1] = min(nxtDp[s][1], dp[u][s][0] + dp[v][1][1]);
nxtDp[s][1] = min(nxtDp[s][1], dp[u][s ^ 1][0] + dp[v][0][1] + 2);
nxtDp[s][2] = min(nxtDp[s][2], dp[u][s][1] + dp[v][1][1]);
nxtDp[s][2] = min(nxtDp[s][2], dp[u][s ^ 1][1] + dp[v][0][1] + 2);
nxtDp[s][2] = min(nxtDp[s][2], dp[u][s][0] + dp[v][0][2] + 1);
nxtDp[s][2] = min(nxtDp[s][2], dp[u][s ^ 1][0] + dp[v][1][2] + 3);
nxtDp[s][2] = min(nxtDp[s][2], dp[u][s ^ 1][2] + dp[v][1][0] + 1);
nxtDp[s][2] = min(nxtDp[s][2], dp[u][s][2] + dp[v][0][0] + 3);
}
for(int s = 0; s < 2; s++)
for(int i = 0; i < 3; i++)
dp[u][s][i] = nxtDp[s][i];
}
}
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cin >> n >> s;
s = '*' + s;
for(int i = 1; i < n; i++){
int u, v;
cin >> u >> v;
adj[u].push_back(v);
adj[v].push_back(u);
}
memset(dp, 0x3f, sizeof(dp));
int root = 1;
Dfs(root, -1);
cout << dp[root][1][2];
return 0;
}
