moortal combat, summits problem <3

#pragma GCC optimize ("O3")
#pragma GCC target("sse4")
#include <bits/stdc++.h>
#define f first
#define s second
#define pb push_back
#define mp make_pair
#define ts to_string
#define ub upper_bound
#define lb lower_bound
const char nl = '\n';
using namespace std;
using ll = long long;
using vi = vector<int>;
using vl = vector<ll>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using str = string;
//The following debugging code was taken from Benjamin Qi's template :)
str ts(char c) { return str(1,c); }
str ts(bool b) { return b ? "true" : "false"; }
str ts(const char* s) { return (str)s; }
str ts(str s) { return s; }
template<class A> str ts(complex<A> c) {
    stringstream ss; ss << c; return ss.str(); }
str ts(vector<bool> v) {
    str res = "{"; for(int i = 0;i < (int)v.size(); i++) res += char('0'+v[i]);
    res += "}"; return res; }
template<size_t SZ> str ts(bitset<SZ> b) {
    str res = ""; for(int i = 0; i < b.size(); i++) res += char('0'+b[i]);
    return res; }
template<class A, class B> str ts(pair<A,B> p);
template<class T> str ts(T v) {
    bool fst = 1; str res = "{";
    for (const auto& x: v) {
        if (!fst) res += ", ";
        fst = 0; res += ts(x);
    }
    res += "}"; return res;
}
template<class A, class B> str ts(pair<A,B> p) {
    return "("+ts(p.f)+", "+ts(p.s)+")"; }
void DBG() { cerr << "]" << endl; }
template<class H, class... T> void DBG(H h, T... t) {
    cerr << ts(h); if (sizeof...(t)) cerr << ", ";
    DBG(t...); }

#ifdef LOCAL
#define dbg(...) cerr << "LINE(" << __LINE__ << ") -> [" << #__VA_ARGS__ << "]: [", DBG(__VA_ARGS__)
#else
#define dbg(...) 0
#endif
//CODE STARTS HERE-----------------------------------------------------------------------------------------//
const int N = 1e5 + 10;
int n, m, k;
int d[26][26];
int dp[N][26];
int p[N][26];
string c;
signed main(){
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    freopen("cowmbat.in", "r", stdin);
    freopen("cowmbat.out", "w", stdout);
    cin >> n >> m >> k >> c;
    for(int i = 0; i < m; i++){
        for(int j = 0; j < m; j++){
            cin >> d[i][j];
        }
    }
    bool flag = 1;
    while(flag){
        flag = 0;
        for(int i = 0; i < m; i++){
            for(int j = 0; j < m; j++){
                for(int k = 0; k < m; k++){
                    if(d[i][j] > d[i][k] + d[k][j]){
                        d[i][j] = d[i][k] + d[k][j];
                        flag=1;
                    }
                }
            }
        }
    }
    // for(int i =0; i < m; i++) for(int j = 0; j < m; j++) dbg(d[i][j], i, j);
    for(int i =1 ; i <=  n; i++){
        for(int j = 0; j < m; j++){
            p[i][j] = d[c[i-1] - 'a'][j];
            if(i) p[i][j] += p[i-1][j];
            // dbg(p[i][j], i, j);
        }
    }
    //o(26 * 1e5 * 26)
    memset(dp, 0x3f, sizeof(dp));
    for(int i=0; i < m; i++) dp[0][i] = 0;
    // for(int i=0; i < m; i++) dp[1][i] = p[1][i];
    for(int i = 1; i <= n; i++){
        if(i >= k){
            for(int j =0 ; j < m;j++){
                for(int a = 0; a < m; a++){
                    dp[i][j] = min(dp[i][j] , dp[i-k][a] + p[i][j] - p[i-k][j]);
                }
            }
        }
        if(i > 1){
            for(int j = 0; j < m; j++){
                dp[i][j] = min(dp[i][j], dp[i-1][j] + p[i][j] - p[i-1][j]);
            }
        }
        // for(int j = 0; j < m; j++) dbg(dp[i][j],i,j);
    }
    int ans = 2e9;
    for(int i=0 ; i < m; i++){
        ans = min(ans, dp[n][i]);
    }
    cout << ans << nl;
}