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

typedef long long ll;
typedef vector< int > vi;
typedef vector< vi > vvi;
typedef vector< ll > vl;
typedef vector< vl > vvl;
typedef pair< int, int > pii;
typedef vector< pii > vp;
typedef vector< double > vd;
typedef vector< vd > vvd;
typedef vector< string > vs;

template< class T1, class T2 >
int upmin( T1 &x, T2 v ){
  if( x > v ){
    x = v;
    return 1;
  }
  return 0;
}

template< class T1, class T2 >
int upmax( T1 &x, T2 v ){
  if( x < v ){
    x = v;
    return 1;
  }
  return 0;
}

const int INF = 0x3f3f3f3f;

int N;
string seq;

vvi G;

void init(){
  cin >> N;
  cin >> seq;
  G = vvi( N );
  for( int i = 0; i < N - 1; ++i ){
    int u, v; cin >> u >> v;
    G[ u - 1 ].emplace_back( v - 1 );
    G[ v - 1 ].emplace_back( u - 1 );
  }
}

const int MAXN = ( int ) 1e5;

ll dp_d[ MAXN + 1 ][ 2 ]; // how many "ww"s / how many "w"s
ll dp_u[ MAXN + 1 ][ 2 ]; 

void dfs_d( int u, int fa ){
  ll ww = 0, w = 0;
  for( int v : G[ u ] ){
    if( v == fa ) continue;
    dfs_d( v, u );
    ww += dp_d[ v ][ 0 ];
    w += dp_d[ v ][ 1 ];
  }
  if( seq[ u ] == 'w' ){
    ww += w;
    ++w;
  }
  dp_d[ u ][ 0 ] = ww;
  dp_d[ u ][ 1 ] = w;
}

void dfs_u( int u, int fa, ll upww, ll upw ){
  dp_u[ u ][ 0 ] = upww;
  dp_u[ u ][ 1 ] = upw;
  for( int v : G[ u ] ){
    if( v == fa ) continue;
    upww += dp_d[ v ][ 0 ];
    upw += dp_d[ v ][ 1 ];
  }
  for( int v : G[ u ] ){
    if( v == fa ) continue;
    ll nupww = upww - dp_d[ v ][ 0 ];
    ll nupw = upw - dp_d[ v ][ 1 ];
    if( seq[ u ] == 'w' ){
      nupww += nupw;
      ++nupw;
    }
    dfs_u( v, u, nupww, nupw );
  }
}

void preprocess(){
  dfs_d( 0, -1 );
  dfs_u( 0, -1, 0, 0 );
}

void solve(){
  ll ans = 0;
  for( int i = 0; i < N; ++i ){
    if( seq[ i ] == 'c' ){
      ans += dp_d[ i ][ 0 ] + dp_u[ i ][ 0 ];
    }
  }
  cout << ans << endl;
}

signed main(){
  ios::sync_with_stdio( 0 );
  init();
  preprocess();
  solve();
  return 0;
}