#include <bits/stdc++.h>

#define MAX 305
#define oo  0x2f2f2f2f

using namespace std;
using ii = pair<int, int>;

char grid[MAX][MAX];
int  free_seats[MAX][MAX];

ii subinterval_sum(int* A, int n, int sum) {
    int current_sum = A[1], start = 1, current_length = oo;
    ii  subinterval(0, 0);
    for(int i = 2; i <= n + 1; ++i) {
        while(current_sum > sum and start <= i) {
            current_sum -= A[start++];
        }
        if(current_sum >= sum) {
            if(current_length > (i - start)) {
                current_length = i - start;
                subinterval = ii(start, i - 1);
            }
            current_sum -= A[start++];
        }
        if(i <= n) {
            current_sum += A[i];
        }
    }
    return subinterval;
}

int main(void) {
    int n, m, k;
    while(scanf("%d %d %d", &n, &m, &k), n | m | k) {
        for(int i = 1; i <= n; ++i) {
            for(int j = 1; j <= m; ++j) {
                scanf(" %c", &grid[i][j]);
            }
        }

        for(int i = 1; i <= n; ++i) {
            for(int j = 1; j <= m; ++j) {
                free_seats[i][j] = grid[i][j] ==  '.';
            }
        }

        int ans = oo;
        for(int i = 1; i <= m; ++i) {
            int tmp[n + 1]; memset(tmp, 0, sizeof tmp);
            for(int j = i; j <= m; ++j) {
                for(int k = 1; k <= n; ++k) {
                    tmp[k] += free_seats[k][j];
                }
                auto s = subinterval_sum(tmp, n, k);
                if(s.first and s.second) {
                    ans = min(ans, (s.second - s.first + 1) * (j - i + 1));
                }
            }
        }
        printf("%d\n", ans);
    }
    return 0;
}