#include<bits/stdc++.h>
using namespace std;
int dp[100001],q[30][100001];
int n,m,k;
string s;
int w[30][30],ans[100001];
int main(){
	freopen("cowmbat.in","r",stdin);
	freopen("cowmbat.out","w",stdout);
	cin>>n>>m>>k;
	cin>>s;
	s=' '+s;
	for(int i=1;i<=m;i++){
		for(int j=1;j<=m;j++){
			cin>>w[i][j];
		}
	}
	for(int k=1;k<=m;k++){//预处理 
		for(int i=1;i<=m;i++){
			for(int j=1;j<=m;j++){
				w[i][j]=min(w[i][k]+w[k][j],w[i][j]);
			}
		}
	}
	for(int i=1;i<=m;i++){
		for(int j=1;j<=n;j++){
			q[i][j]=w[s[j]-'a'+1][i]+q[i][j-1];
		}
	}
	memset(ans,0x3f,sizeof(ans));
	memset(dp,0x3f,sizeof(dp));
	dp[0]=0;
	for(int i=1;i<=n;i++){
		for(int j=1;j<=m;j++){
			if(i>=k)ans[j]=min(ans[j],dp[i-k]-q[j][i-k]);
			dp[i]=min(dp[i],ans[j]+q[j][i]);
		}
	}
	cout<<dp[n];
	fclose(stdin);
	fclose(stdout);
	return 0;
}