/*

This Submission is to determine how many 120/240 min const. delivery point there are.

//info
120 req. steps <= 5

test_case 1,6 == 50 delivery point
		 2,3,4,5,7 == 80 delivery point
				8,9 == 90 delivery point
				10 > 100 delivery point
*/
#define  _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <algorithm>
#include <utility>
#include <functional>
#include <cstring>
#include <queue>
#include <stack>
#include <math.h>
#include <iterator>
#include <vector>
#include <string>
#include <set>
#include <math.h>
#include <iostream>
#include <random>
#include<map>
#include <iomanip>
#include <time.h>
#include <stdlib.h>
#include <list>
#include <typeinfo>
#include <list>
#include <set>
#include <cassert>
#include<fstream>
#include <unordered_map>
#include <cstdlib>
#include <complex>
#include <cctype>
#include <bitset>
using namespace std;
typedef string::const_iterator State;
#define Ma_PI 3.141592653589793
#define eps 0.00000001
#define LONG_INF 1e18
#define GOLD 1.61803398874989484820458
#define MAX_MOD 1000000007
#define MOD 1000000007
#define seg_size 262144
#define REP(a,b) for(long long a = 0;a < b;++a)

unsigned long xor128() {
	static unsigned long x = time(NULL), y = 362436069, z = 521288629, w = 88675123;
	unsigned long t = (x ^ (x << 11));
	x = y; y = z; z = w;
	return (w = (w ^ (w >> 19)) ^ (t ^ (t >> 8)));
}
long long h, w;
int cnt[2002][2002][26];
long long func(long long k) {
	long long ans = 0;
	for (int left = 0;left < w; ++left) {
		for (int right = left + 1; right <= w; ++right) {
			long long classic[26] = {};
			long long now_cnt = 0;
			for (int j = 0; j < h; ++j) {
				REP(t, 26) {
					if (classic[t] == 0) {
						classic[t] += cnt[j][right][t] - cnt[j][left][t];
						if (classic[t] != 0)now_cnt++;
					}
					else {
						classic[t] += cnt[j][right][t] - cnt[j][left][t];
					}
				}
				if (j - (right - left) >= 0) {
					REP(t, 26) {
						if (classic[t] != 0) {
							classic[t] -= cnt[j - (right - left)][right][t] - cnt[j - (right - left)][left][t];
							if (classic[t] == 0)now_cnt--;
						}
						else {
							classic[t] -= cnt[j - (right - left)][right][t] - cnt[j - (right - left)][left][t];
						}
					}
				}
				if (j >= (right - left - 1LL)) {
					if (now_cnt == k) ans++;
				}
			}
		}
	}
	return ans;
}
int main(){
	long long k;
	cin >> h >> w >> k;
	for (int i = 0; i < h;++i) {
		string a;
		cin >> a;
		for (int q = 1; q <= w; ++q) {
			REP(j, 26) {
				cnt[i][q][j] += cnt[i][q - 1][j];
			 }
			cnt[i][q][a[q - 1] - 'a']++;
		}
	}
	cout << func(k) << endl;
	return 0;
}