#define rep(i, n) for(int i = 0; i < (int)(n); i++)
typedef int ll;
#include <bits/stdc++.h>
using namespace std;
int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    ll h,w,K;
    std::cin >> h>>w>>K;
    std::vector<string> s(h);
    ll sum[26][2001][2001];
    
    // vector<vector<vector<ll>>> sum(26,vector<vector<ll>>(h+1,vector<ll>(w+1)));
    for (int i = 0; i < h; i++) {
        std::cin >> s[i];
        for (int j = 0; j < w; j++) {
            int alpha = s[i][j]-'a';
            for (int k = 0; k < 26; k++) {
                sum[k][i+1][j+1] = sum[k][i][j+1] + sum[k][i+1][j] - sum[k][i][j];
            }
            sum[alpha][i+1][j+1]++;
        }
    }
    ll result = 0;
    vector<vector<ll>> size_from(h,vector<ll>(w,1));
    
    for (int i = 0; i < h; i++) {
        for (int j = 0; j < w; j++) {
            for (int size = size_from[i][j]; i+size<h && j+size<w; size++) {
                ll num = 0;
                for (int k = 0; k < 26; k++) {
                    ll cou;
                    cou = sum[k][i+size+1][j+size+1]-sum[k][i][j+size+1]-sum[k][i+size+1][j]+sum[k][i][j];
                    if(cou>0){
                        num++;
                    }
                }
                if(num<K && size>1){
                    if(i+1<h)size_from[i+1][j] = size;
                    if(j+1<w)size_from[i][j+1] = size;
                    if(j+1<w && i+1<h)size_from[i][j+1] = size;
                }
                if(num==K){
                    result++;
                }
                if(num>K){
                    break;
                }
            }
            
        }
    }
    std::cout << result << std::endl;
}