#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N=100010;
int n,m,k,a[N],dis[110][110],s[110][N],f[N],ans[N];
ll res=1e18;
int main () {
	freopen("cowmbat.in","r",stdin);
	freopen("cowmbat.out","w",stdout);
	ios::sync_with_stdio(0);
	cin.tie(0),cout.tie(0);
	memset(f,0x3f,sizeof(f));
	memset(ans,0x3f,sizeof(ans));
	cin >> n >> m >> k;
	for (int i=1;i<=n;i++) {
		char c;
		cin >> c;
		a[i]=int(c)-96;
		//cout << a[i] <<' ';
	}
	for (int i=1;i<=m;i++) {
		for (int j=1;j<=m;j++) {
			cin >> dis[i][j];
		}
	}
	for (int k=1;k<=m;k++) {
		for (int i=1;i<=m;i++) {
			for (int j=1;j<=m;j++) {
				dis[i][j]=min(dis[i][j],dis[i][k]+dis[k][j]);
			}
		}
	}
	//cout << dis[4][3] <<endl;
	for (int i=1;i<=m;i++) {
		for (int j=1;j<=n;j++) {
			s[i][j]=dis[a[j]][i]+s[i][j-1];
		}
	}
	ans[0]=0;
	for (int i=k;i<=n;i++) {
		for (int j=1;j<=m;j++) {
			f[j]=min(f[j]+dis[a[i]][j],ans[i-k]+s[j][i]-s[j][i-k]);
			ans[i]=min(ans[i],f[j]);
		}
	}
	cout << ans[n] <<endl;
	return 0;
}