#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <queue>
#include <string>
#include <map>
#include <set>
#include <stack>
#include <tuple>
#include <deque>
#include <array>
#include <numeric>
#include <bitset>
#include <iomanip>
#include <cassert>
#include <chrono>
#include <random>
#include <limits>
#include <iterator>
#include <functional>
#include <sstream>
#include <fstream>
#include <complex>
#include <cstring>
#include <unordered_map>
#include <unordered_set>
using namespace std;

using ll = long long;
constexpr int INF = 1001001001;
constexpr int mod = 1000000007;
// constexpr int mod = 998244353;

template<class T>
inline bool chmax(T& x, T y){
    if(x < y){
        x = y;
        return true;
    }
    return false;
}
template<class T>
inline bool chmin(T& x, T y){
    if(x > y){
        x = y;
        return true;
    }
    return false;
}

template<typename T>
struct CumulativeSum2D{
    vector<vector<T>> data;

    CumulativeSum2D(int W, int H) : data(W + 1, vector<T>(H + 1, 0)) {}

    void add(int x, int y, T z){
        ++x, ++y;
        if(x >= data.size() || y >= data[0].size()) return;
        data[x][y] += z;
    }

    void build(){
        for(int i = 1; i < (int)data.size(); ++i){
            for(int j = 1; j < (int)data[i].size(); ++j){
                data[i][j] += data[i][j - 1] + data[i - 1][j] - data[i - 1][j - 1];
            }
        }
    }

    T query(int sx, int sy, int gx, int gy){
        return (data[gx][gy] - data[sx][gy] - data[gx][sy] + data[sx][sy]);
    }
};

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int H, W, K;
    cin >> H >> W >> K;
    vector<CumulativeSum2D<int>> S(26, CumulativeSum2D<int>(H, W));
    vector<vector<char>> c(H, vector<char>(W));
    for(int i = 0; i < H; ++i){
        for(int j = 0; j < W; ++j){
            cin >> c[i][j];
            S[c[i][j] - 'a'].add(i, j, 1);
        }
    }
    for(int i = 0; i < 26; ++i) S[i].build();

    int ans = 0;
    for(int x = 0; x < H; ++x){
        for(int y = 0; y < W; ++y){
            for(int i = 1; i <= min(H, W); ++i){
                if(x + i > H || y + i > W)  continue;
                int cnt = 0;
                for(int j = 0; j < 26; ++j){
                    cnt += S[j].query(x, y, x + i, y + i) > 0;
                }
                if(cnt > K) break;
                ans += cnt == K;
            }
        }
    }

    cout << ans << endl;

    return 0;
}