#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pii pair<int,int>
#define pb push_back
#define eb emplace_back
#define all(x) (x).begin(), (x).end()
#define fi first
#define se second
#define endl '\n'
#define task "2"
const int MN = 2e5+5;
int n,u,v,has_power[MN],pa[MN],h[MN],ans;
vector<int> adj[MN],generators;
void dfs(int u,int p){
pa[u] = p;
h[u] = h[p] + 1;
for(auto v:adj[u]) if(v!=p) dfs(v,u);
}
signed main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cin >> n;
if(n>20){
cerr << "N IS TOO BIG: N = " << n << endl;
return 0;
}
for(int i=1; i<n; i++){
cin >> u >> v;
adj[u].pb(v);
adj[v].pb(u);
}
string s; cin >> s;
for(int i=1; i<=n; i++) if(s[i-1]=='1'){
generators.pb(i);
has_power[i] = 1;
}
dfs(1,0);
int sz = generators.size();
for(int mask=0; mask<(1<<sz); mask++){
bitset<20> activated = 0, broken = 0;
vector<int> filtered;
for(int i=0; i<sz; i++) if(1&(mask>>i)) filtered.push_back(generators[i]);
for(auto u:filtered) activated[u] = 1;
for(auto u:filtered){
for(auto v:filtered){
if(u>=v) continue;
vector<int> path;
int x = u, y = v;
if(h[x]<h[y]) swap(x,y);
while(h[x]>h[y]){
x = pa[x];
if(x!=y) path.pb(x);
}
while(x!=y){
x = pa[x]; y = pa[y];
path.pb(x);
if(x!=y) path.pb(y);
}
for(auto x:path) if(has_power[x]) activated[x] = 0, broken[x] = 1;
// cerr << "PATH: " << u << ' ' << v << ": ";
// for(auto x:path) cerr << x << ' '; cerr << endl;
}
}
ans = max(ans,(int)activated.count()-(int)broken.count());
}
cout << ans;
cerr << "\nThoi gian loj: " << clock() << endl;
}
