#include <bits/stdc++.h>
using namespace std;
const int N = 1e2 + 5;
const int INF = 1e9;
vector<int> Graph[N];
bool Active[N];
bool Full[N];
pair<int, int> DP[N][2];
bool PreDFS(int u, int parent)
{
Full[u] = Active[u];
for(auto v : Graph[u]) {
if(v != parent)
Full[u] &= PreDFS(v, u);
}
return Full[u];
}
void DFS(int u, int parent)
{
bool ac = !Active[u];
DP[u][0].first = 1;
DP[u][1].first = 1;
for(auto v : Graph[u]) {
if(v != parent && !Full[v]) {
DFS(v, u);
DP[u][0].first += DP[v][0].first + 1;
ac ^= 1;
if(DP[v][0].second == 0) {
DP[u][0].first += 2;
ac ^= 1;
}
}
}
DP[u][0].second = ac;
DP[u][1] = DP[u][0];
if(!ac)
DP[u][1] = {DP[u][1].first - 1, 1};
for(auto v : Graph[u]) {
if(v != parent && !Full[v]) {
int val = DP[u][0].first - DP[v][0].first + DP[v][1].first - 1;
bool ac2 = !ac;
if(DP[v][0].second == 0) {
val -= 2;
ac2 = !ac2;
}
if(ac2)
DP[u][1].first = min(DP[u][1].first, val);
}
}
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(0);
int n, a, b;
string s;
cin >> n >> s;
for(int i = 0; i < n-1; i++) {
cin >> a >> b;
Graph[a].push_back(b);
Graph[b].push_back(a);
}
for(int i = 0; i < s.size(); i++)
Active[i+1] = (s[i] == '1');
int sol = INF;
for(int i = 1; i <= n; i++) {
PreDFS(i, 0);
DFS(i, 0);
sol = min(sol, DP[i][1].first);
}
cout << sol;
}
