#include<bits/stdc++.h> using namespace std; using Int = long long; template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;} template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;} //INSERT ABOVE HERE signed main(){ Int n; string s; cin>>n>>s; vector<vector<Int> > G(n); for(Int i=1;i<n;i++){ Int x,y; cin>>x>>y; x--;y--; G[x].emplace_back(y); G[y].emplace_back(x); } vector<Int> w(n,0),ww(n,0); { function<void(Int, Int)> dfs= [&](Int v,Int p){ w[v]=s[v]=='w'; for(Int u:G[v]){ if(u==p) continue; dfs(u,v); w[v]+=w[u]; ww[v]+=ww[u]; if(s[v]=='w') ww[v]+=w[u]; } }; dfs(0,-1); } Int ans=0,wa=0; for(Int i=0;i<n;i++) wa+=s[i]=='w'; function<void(Int, Int, Int)> dfs= [&](Int v,Int p,Int x){ //cout<<v<<":"<<x<<" "<<ww[v]<<endl; if(s[v]=='c') ans+=x+ww[v]; for(Int u:G[v]){ if(u==p) continue; if(s[v]=='c') dfs(u,v,x+(ww[v]-ww[u])); else dfs(u,v,x+(ww[v]-(w[v]-1)-ww[u])+(wa-w[v])); } }; dfs(0,-1,0); cout<<ans<<endl; return 0; }