#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N=100005;
int n,ans,c[N],w[N],f[N];string s;
vector<int>g[N];
void dfs(int u,int fa)
{
	f[u]=fa;
	if(s[u-1]=='c')c[u]=1;
	else w[u]=1;
	for(int v:g[u])
	{
		if(v==fa)continue;
		dfs(v,u);c[u]+=c[v];w[u]+=w[v];
	}
}
signed main()
{
	cin>>n>>s;
	for(int i=1,u,v;i<n;i++)
	{
		cin>>u>>v;
		g[u].push_back(v);
		g[v].push_back(u);
	}
	dfs(1,0);
	for(int i=1,x,y,z;i<=n;i++)
	{
		x=0;y=0;z=0;
		for(int v:g[i])
		{
			if(v==f[i])continue;
			x+=c[v];y+=w[v];z+=c[v]*w[v];
		}
		x+=c[1]-c[i];
		y+=w[1]-w[i];
		z+=(c[1]-c[i])*(w[1]-w[i]);
		ans+=x*y-z;
	}
	cout<<ans; 
}