DELTREE

//Nguyen Huu Hoang Minh
#include <bits/stdc++.h>
#define sz(x) int(x.size())
#define all(x) x.begin(),x.end()
#define reset(x) memset(x, 0,sizeof(x))
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define N 300005
#define remain(x) if (x > MOD) x -= MOD
#define ii pair<int, int>
#define iiii pair< ii , ii >
#define viiii vector< iiii >
#define vi vector<int>
#define vii vector< ii >
#define bit(x, i) (((x) >> (i)) & 1)
#define Task "deltree"
#define int long long

using namespace std;

typedef long double ld;
const int inf = 1e10;
const int minf = -1e10;

int n;
string s;
vector<int> g[N];
int dp[N][2];

void readfile()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);cout.tie(0);
    if (fopen(Task".inp","r"))
    {
        freopen(Task".inp","r",stdin);
        freopen(Task".out","w",stdout);
    }
    cin >> n >> s;
    s = " " + s;
    for(int i=1; i<n; i++){
        int u, v; cin >> u >> v;
        g[u].pb(v);
        g[v].pb(u);
    }
}

void dfs(int u, int par){
    for(auto v : g[u]){
        if (v==par) continue;
        dfs(v,u);
        dp[u][0] += min(dp[v][0],dp[v][1]+1);
        dp[u][1] += min(dp[v][1],dp[v][0]+1);
    }
    dp[u][0] += ((s[u]-'0')==0 ? 0 : 1);
    dp[u][1] += ((s[u]-'0')==1 ? 0 : 1);
}

void proc()
{
    dfs(1,-1);
    cout << min(dp[1][0],dp[1][1])+1;
}

signed main()
{
    readfile();
    proc();
    return 0;
}