//Accepted    15880 KB    250 ms
 #include <cstdio>
 #include <cstring>
 #include <iostream>
 using namespace std;
 ;
 ;
 ;
 int dp[imax_n][imax_n];
 int addcost[imax_m];
 int deletecost[imax_m];
 int n;
 int m;
 char s[imax_n];
 int min(int a,int b)
 {
     return a<b?a:b;
 }
 void Dp()
 {
     memset(dp,,sizeof(dp));
     //for (int i=1;i<=n;i++)
     //dp[i][i]=0;
     ;l<=n;l++)
     {
         ;i<=n;i++)
         {
             ;
             dp[i][j]=inf;
             ]==s[j-]) dp[i][j]=dp[i+][j-];
             dp[i][j]=min(dp[i][j],dp[i+][j]+addcost[s[i-]-'a']);
             dp[i][j]=min(dp[i][j],dp[i+][j]+deletecost[s[i-]-'a']);
             dp[i][j]=min(dp[i][j],dp[i][j-]+addcost[s[j-]-'a']);
             dp[i][j]=min(dp[i][j],dp[i][j-]+deletecost[s[j-]-'a']);
         }
     }
     printf(][n]);
 }
 int main()
 {
     //while (scanf("%d%d",&m,&n)!=EOF)
     {
         scanf("%d%d",&m,&n);
         scanf("%s",s);
         ];
         memset(addcost,,sizeof(addcost));
         memset(deletecost,,sizeof(deletecost));
         ;i<=m;i++)
         {
             scanf("%s",ss);
             scanf(]-]-'a']);
         }
         Dp();
     }
     ;
 }