#pragma GCC optimize("O3")
#pragma GCC optimize ("unroll-loops")
#pragma GCC target("avx,avx2,fma")
#include <bits/stdc++.h>

typedef long double ld;
typedef long long ll;
using namespace std;
int di[] = {1, 0, -1, -1, 0, 1, -1, 1};
int dj[] = {1, 1, 0, -1, -1, 0, 1, -1};
const ll oo = 1e18, MOD = 998244353;
const int N = 1e5 + 5, M = 350;
const ld PI = acos(-1.0), EPS = 1e-9;

//#define endl '\n'
int main() {
    ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    //freopen("farm.in", "r", stdin);
    //memset(dp, -1, sizeof dp);
    int n, m;
    cin >> n >> m;
    int a[n + 5][m + 5][26];
    for (int i = 0; i <= n; i++) for (int j = 0; j <= m; j++) for (int k = 0; k < 26; k++) a[i][j][k] = 0;
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            char c;
            cin >> c;
            a[i][j][c - 'A']++;
        }
    }
    for (int k = 0; k < 26; k++) {
        for (int i = 1; i <= n; i++) {
            for (int j = 1; j <= m; j++) a[i][j][k] += a[i][j - 1][k];
        }
        for (int j = 1; j <= m; j++) {
            for (int i = 1; i <= n; i++) a[i][j][k] += a[i - 1][j][k];
        }
    }
    int ans = 1e9;
    if (n < m) {
        for (int i = 1; i <= n; i++) {
            for (int j = 1; j <= m; j++) {
                for (int k = i; k <= n; k++) {
                    int l = j, r = m, mid, xl = i, xr = k, yl = j, yr = 0;
                    while (l <= r) {
                        mid = (l + r) >> 1;
                        int num1 = a[k][mid][0] - a[k][yl - 1][0] - a[xl - 1][mid][0] + a[xl - 1][yl - 1][0];
                        int num2 = a[k][mid][3] - a[k][yl - 1][3] - a[xl - 1][mid][3] + a[xl - 1][yl - 1][3];
                        int num3 = a[k][mid][11] - a[k][yl - 1][11] - a[xl - 1][mid][11] + a[xl - 1][yl - 1][11];
                        int num4 = a[k][mid][14] - a[k][yl - 1][14] - a[xl - 1][mid][14] + a[xl - 1][yl - 1][14];
                        int num5 = a[k][mid][22] - a[k][yl - 1][22] - a[xl - 1][mid][22] + a[xl - 1][yl - 1][22];
                        if (!num1 || !num2 || !num3 || !num4 || !num5) l = mid + 1;
                        else yr = mid, r = mid - 1;
                    }
                    if (!yr) continue;
                    ans = min(ans, (xr - xl + 1) * (yr - yl + 1));
                }
            }
        }
    } else {
        for (int i = 1; i <= n; i++) {
            for (int j = 1; j <= m; j++) {
                for (int k = j; k <= m; k++) {
                    int l = i, r = n, mid, xl = i, xr = 0, yl = j, yr = k;
                    while (l <= r) {
                        mid = (l + r) >> 1;
                        int num1 = a[mid][yr][0] - a[mid][yl - 1][0] - a[xl - 1][yr][0] + a[xl - 1][yl - 1][0];
                        int num2 = a[mid][yr][3] - a[mid][yl - 1][3] - a[xl - 1][yr][3] + a[xl - 1][yl - 1][3];
                        int num3 = a[mid][yr][11] - a[mid][yl - 1][11] - a[xl - 1][yr][11] + a[xl - 1][yl - 1][11];
                        int num4 = a[mid][yr][14] - a[mid][yl - 1][14] - a[xl - 1][yr][14] + a[xl - 1][yl - 1][14];
                        int num5 = a[mid][yr][22] - a[mid][yl - 1][22] - a[xl - 1][yr][22] + a[xl - 1][yl - 1][22];
                        if (!num1 || !num2 || !num3 || !num4 || !num5) l = mid + 1;
                        else xr = mid, r = mid - 1;
                    }
                    if (!xr) continue;
                    ans = min(ans, (xr - xl + 1) * (yr - yl + 1));
                }
            }
        }
    }
    if (ans == 1e9) cout << "impossible";
    else cout << ans;
    return 0;
}