#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstring>
#include<algorithm>
#include<cassert>
#include<utility>
#include<queue>
#include<stack>
#include<vector>
#include<map>
#include<set>
#include<bitset>
 
#define rep(i,l,r) for(int i=(l);i<=(r);i++)
#define per(i,r,l) for(int i=(r);i>=(l);i--)
 
#define all(vc) vc.begin(),vc.end()
#define sz(vc) ((int)vc.size())
#define pb push_back
#define fi first
#define se second
#define x0 __x00
#define y0 __y00
 
using namespace std;
 
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
 
const int N=1e5+5;
string s;
int n,w,c,f[N],g[N];
vector<int>G[N];
ll ans;
 
void dfs(int x,int fa){
    f[x]+=s[x]=='w';
    g[x]+=s[x]=='c';
    for(auto to:G[x]){
        if(to==fa)continue;
        dfs(to,x);
        f[x]+=f[to],g[x]+=g[to];
    }
    if(s[x]=='c')return;
    for(auto to:G[x]){
        if(to==fa)continue;
        ans+=1ll*g[x]*(w-f[to]-1);
    }
    ans+=1ll*(f[x]-1)*(c-g[x]);
}
 
 
int main(){
 
 
    ios::sync_with_stdio(0);
    cin.tie(0),cout.tie(0);
     
 
    cin>>n>>s;
    s=' '+s;
    rep(i,2,n){
        int u,v;cin>>u>>v;
        G[u].pb(v);G[v].pb(u);
    }
    rep(i,1,n)w+=s[i]=='w',c+=s[i]=='c';
 
    dfs(1,-1);
 
    cout<<ans<<'\n';
 
 
    return 0;
}