#include <iostream>

 #include <cstdio>

 using namespace std;

 int n,m;

 int cost[];

 int dp[][];

 int main()

 {

     string s;

     int x,y;

     char z;

     cin >> n >> m >> s;

     for(int i = ; i < n; i++)

     {

         cin >> z >> x >> y;

         cost[z - 'a'] = min(x, y);

     }

     for(int i = m-; i >= ; i--)

     {

         for(int j = i+; j < m; j++)

         {

             if(s[i] == s[j])

             {

                 dp[i][j] = dp[i+][j-];

             }

             else

             {

                 dp[i][j] = min(dp[i+][j] + cost[s[i] - 'a'],

                                dp[i][j-] + cost[s[j] - 'a']);

             }

         }

     }

     cout << dp[][m-] << endl;

     return ;

 }