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#include <iostream>
#include <vector>
#include <queue>
#include <cstring>
#include <algorithm>
#include <fstream>
using namespace std;
int n;
char mat[22][22];
int dp[1 << 21];
int bitmask_mat[22];
int rec(int bitmask) {
    if(__builtin_popcount(bitmask) == n) {
        return 0;
    }
    if(dp[bitmask] != -1) {
        return dp[bitmask];
    }
    int result = 2e9;
    for(int i = 0; i < n; i++) {
        if(bitmask & (1 << i)){
            continue;
        }
        int changes = __builtin_popcount(bitmask & bitmask_mat[i]);
       
        result = min(result, rec(bitmask | (1 << i)) + changes);
    }
    return dp[bitmask] = result;
}
int main() {
    ios_base::sync_with_stdio(false);
    cin >> n;
    for(int i = 0; i < n; i++) {
        for(int j = 0; j < n; j++) {
            cin >> mat[i][j];
        }
        int number = 0;
        for(int j = n - 1; j >= 0; j--) {
            if(mat[i][j] == 'D'){
                number |= (1 << j);
            }
        }
        bitmask_mat[i] = number;
    }
    memset(dp, -1, sizeof dp);
    cout << rec(0) << endl;

return 0;
}