#include<bits/stdc++.h>
using namespace std;
const int N=1e5+5;
int n,m,k,a[35][35],f[N],b[35],sum[35][N];
char s[N];
int main(){
	freopen("cowmbat.in","r",stdin);
	freopen("cowmbat.out","w",stdout);
	scanf("%d%d%d",&n,&m,&k);
	for(int i = 1;i<=n;i++) cin>>s[i];
	for(int i = 1;i<=m;i++)
	for(int j = 1;j<=m;j++)
	scanf("%d",&a[i][j]);
	for(int l = 1;l<=m;l++)
	for(int i = 1;i<=m;i++)
	for(int j = 1;j<=m;j++)
	a[i][j]=min(a[i][j],a[i][l]+a[l][j]);
	for(int i = 1;i<=n;i++)
	for(int j  =1;j<=m;j++)
	sum[j][i]=a[s[i]-'a'+1][j]+sum[j][i-1];
	memset(f,0x3f3f3f3f,sizeof(f)); f[0]=0;
	memset(b,0x3f3f3f3f,sizeof(b));
	for(int i = k;i<=n;i++){
		for(int j = 1;j<=m;j++){
			int tmp=sum[j][i]-sum[j][i-k];
			b[j]=min(f[i-k]+tmp,b[j]+a[s[i]-'a'+1][j]);
			f[i]=min(f[i],b[j]);
		}
	}
	printf("%d",f[n]);
	return 0;
}