#include <bits/stdc++.h>
using namespace std;

typedef long long   signed int LL;
typedef long long unsigned int LU;

#define incID(i, l, r) for(int i = (l)    ; i <  (r); i++)
#define incII(i, l, r) for(int i = (l)    ; i <= (r); i++)
#define decID(i, l, r) for(int i = (r) - 1; i >= (l); i--)
#define decII(i, l, r) for(int i = (r)    ; i >= (l); i--)
#define  inc(i, n) incID(i, 0, n)
#define inc1(i, n) incII(i, 1, n)
#define  dec(i, n) decID(i, 0, n)
#define dec1(i, n) decII(i, 1, n)

#define inII(v, l, r) ((l) <= (v) && (v) <= (r))
#define inID(v, l, r) ((l) <= (v) && (v) <  (r))

#define PB push_back
#define EB emplace_back
#define MP make_pair
#define FI first
#define SE second
#define UB upper_bound
#define LB lower_bound
#define PQ priority_queue

#define  ALL(v)  v.begin(),  v.end()
#define RALL(v) v.rbegin(), v.rend()
#define  FOR(it, v) for(auto it =  v.begin(); it !=  v.end(); ++it)
#define RFOR(it, v) for(auto it = v.rbegin(); it != v.rend(); ++it)

template<typename T> bool   setmin(T & a, T b) { if(b <  a) { a = b; return true; } else { return false; } }
template<typename T> bool   setmax(T & a, T b) { if(b >  a) { a = b; return true; } else { return false; } }
template<typename T> bool setmineq(T & a, T b) { if(b <= a) { a = b; return true; } else { return false; } }
template<typename T> bool setmaxeq(T & a, T b) { if(b >= a) { a = b; return true; } else { return false; } }
template<typename T> T gcd(T a, T b) { return (b == 0 ? a : gcd(b, a % b)); }
template<typename T> T lcm(T a, T b) { return a / gcd(a, b) * b; }

// ---- ----

int n;
string s;
vector<int> v[100000];

LL    c[100001];
LL    w[100001];
LL   cw[100001];
LL   ww[100001];
LL  cww[100001];
LL  cPw[100001];
LL cPww[100001];
LL cwPw[100001];

void dfs(int x, int pre) {
	inc(i, v[x].size()) {
		if(v[x][i] == pre) { continue; }
		dfs(v[x][i], x);
	}
	
	cww[x] +=
		(c[x] * ww[x] - cPww[x]) +
		(cw[x] * w[x] - cwPw[x]) +
		(s[x] == 'c' ? ww[x] : (c[x] * w[x] - cPw[x]) + cw[x])
	;
	if(s[x] == 'w') {
		cw[x] += c[x];
		ww[x] += w[x];
	}
	(s[x] == 'c' ? c[x] : w[x]) += 1;
	
	c[pre] += c[x];
	w[pre] += w[x];
	cw[pre] += cw[x];
	ww[pre] += ww[x];
	cww[pre] += cww[x];
	
	cPw[pre] += c[x] * w[x];
	cPww[pre] += c[x] * ww[x];
	cwPw[pre] += cw[x] * w[x];
}

int main() {
	cin >> n >> s;
	inc(i, n - 1) {
		int a, b;
		cin >> a >> b;
		a--; b--;
		v[a].PB(b);
		v[b].PB(a);
	}
	
	dfs(0, n);
	
	cout << cww[0] << endl;
	
	return 0;
}