#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 5;
const int INF = 0x3f3f3f3f;
int mapp[30][30]; 
int sum[30][N];   
int a[30];       
int f[N];          
int n, m, k;
string s;
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 >> mapp[i][j];
        }
    }
    for (int kk = 1; kk <= m; kk++) {
        for (int i = 1; i <= m; i++) {
            for (int j = 1; j <= m; j++) {
                mapp[i][j] = min(mapp[i][j], mapp[i][kk] + mapp[kk][j]);
            }
        }
    }
    for (int c = 1; c <= m; c++) {
        sum[c][0] = 0;
        for (int i = 1; i <= n; i++) {
            sum[c][i] = sum[c][i-1] + mapp[s[i]-'a'+1][c];
        }
    }
    memset(a, 0, sizeof(a));
    memset(f, 0x3f, sizeof(f));
    f[0] = 0;
    for (int i = 1; i <= n; i++) {
        int min_f = INF;
        for (int j = 1; j <= m; j++) {
            a[j] += mapp[s[i]-'a'+1][j];
            if (i >= k) {
                a[j] = min(a[j], f[i - k] + (sum[j][i] - sum[j][i - k]));
            }
            if (i >= k) {
                min_f = min(min_f, a[j]);
            }
        }
        if (i >= k) {
            f[i] = min_f;
        }
    }

    cout << f[n] << "\n";
    return 0;
}