#define _USE_MATH_DEFINES
#include "bits/stdc++.h"
using namespace std;
#define FOR(i,j,k) for(int (i)=(j);(i)<(int)(k);++(i))
#define rep(i,j) FOR(i,0,j)
#define each(x,y) for(auto &(x):(y))
#define mp make_pair
#define MT make_tuple
#define all(x) (x).begin(),(x).end()
#define debug(x) cout<<#x<<": "<<(x)<<endl
#define smax(x,y) (x)=max((x),(y))
#define smin(x,y) (x)=min((x),(y))
#define MEM(x,y) memset((x),(y),sizeof (x))
#define sz(x) (int)(x).size()
#define RT return
using ll = long long;
using pii = pair<int, int>;
using vi = vector<int>;
using vll = vector<ll>;

int bitcnt(unsigned int x) {
    x = (x & 0x55555555) + (x >> 1 & 0x55555555);
    x = (x & 0x33333333) + (x >> 2 & 0x33333333);
    x = (x & 0x0f0f0f0f) + (x >> 4 & 0x0f0f0f0f);
    x = (x & 0x00ff00ff) + (x >> 8 & 0x00ff00ff);
    x = (x & 0x0000ffff) + (x >> 16 & 0x0000ffff);
    return (int)x;
}

using ui = unsigned int;

const int MA = 2001;
ui input[MA][MA], yoko[MA][MA], tate[MA][MA], square[MA][MA];
short cnt[1 << 26];
//      4294967295
// cnt: 2668667000

void solve() {
    int H, W, K;
    cin >> H >> W >> K;

    rep(i, 1 << 26)cnt[i] = bitcnt(i);

    ui ans = 0;
    
    rep(y, H)rep(x, W) {
        char c;
        cin >> c;
        input[y][x] = 1u << (c - 'a');
        yoko[y][x] = tate[y][x] = square[y][x] = input[y][x];
    }
    if (K == 1)ans += (ui)(H * W);
    
    for (int len = 2; len <= min(H, W); ++len) {
        for (int y = 0; y + len <= H; ++y) {
            for (int x = 0; x + len <= W; ++x) {
                yoko[y + len - 1][x] |= input[y + len - 1][x + len - 1];
                tate[y][x + len - 1] |= input[y + len - 1][x + len - 1];
                square[y][x] |= yoko[y + len - 1][x] | tate[y][x + len - 1];

                if (cnt[square[y][x]] == K) {
                    ans++;
                }
            }
        }
    }

    cout << ans << endl;
}

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout << fixed << setprecision(15);
	solve();
	return 0;
}