#include <bits/stdc++.h>
using namespace std;
using ll = long long;

char mp[202][202];
const int dx[] = {-1,-1,-1,0,0,1,1,1}, dy[] = {-1,0,1,-1,1,-1,0,1};

struct st{
    int x, y, d;
};

int main(){
    cin.tie(nullptr)->sync_with_stdio(0);
    int n,m,k, c = 0;
    cin >> n >> m >> k;
    queue<st> q;
    memset(mp, '.', sizeof mp);
    for (int i = 81; i <= n+80; i++){
        for (int j = 81; j <= m+80; j++){
            cin >> mp[i][j];
            if (mp[i][j] == '#'){
                c++;
                q.push({j,i,0});
            }
        }
    }
    if (!c){
        cout << 0;
        return 0;
    }
    int bef = 0, aa = c;
    vector<int> diff;
    while (q.size() and q.front().d < 50){
        int x,y,d;
        x = q.front().x;
        y = q.front().y;
        d = q.front().d;
        q.pop();
        if (d != bef){
            diff.push_back(c - aa);
            // cout << aa << ' ' << c << ' ' << diff.back() << endl;
            bef = d;
            aa = c;
        }
        if (d == k){
            cout << c;
            return 0;
        }
        for (int i = 0; i < 8; i++){
            int nx = x + dx[i], ny = y + dy[i];
            if (mp[ny][nx] != '#'){
                mp[ny][nx] = '#';
                c++;
                q.push({nx, ny, d+1});
            }
        }
    }
    // cout << c << endl;
    // if (k == 50) {
    //     cout << c;
    //     return 0;
    // }
    ll cha = diff.back() - diff[diff.size()-2];
    // cout << c - aa << ' ' << cha <<endl;
    // assert(c - aa -  == cha)?;
    ll ccc = k - 50;
    cout << c + (c-aa)*ccc + (ccc+1)*ccc/2 * cha;
}