#include<cstdio>
#include<vector>
using namespace std;
const int N=1e5+10; vector<int>g[N]; int sumc[N],sumw[N],totc,totw; long long ans; char s[N];
void dfs(int u,int fa) {
  s[u]=='c'?sumc[u]++:sumw[u]++;
  for(auto v:g[u]) {
  	if(v==fa) continue;
  	dfs(v,u),sumc[u]+=sumc[v],sumw[u]+=sumw[v];
  	if(s[u]=='w') ans+=1ll*sumc[v]*(totw-sumw[v]-1);
  }
  if(fa&&s[u]=='w') ans+=1ll*(totc-sumc[u])*(sumw[u]-1); 
}
int main() {
  //freopen("cww.in","r",stdin);
  //freopen("cww.out","w",stdout);
  int n; scanf("%d %s",&n,s+1);
  for(int i=1;i<=n;i++) s[i]=='c'?totc++:totw++;
  for(int i=1,u,v;i<n;i++) scanf("%d %d",&u,&v),g[u].push_back(v),g[v].push_back(u);
  dfs(1,0),printf("%lld",ans);
  return 0;
}