#include <iostream>
#include <fstream>
#include <vector>
#include <map>
#include <cstring>
#include <queue>
#include <algorithm>
//#include <bits/stdc++.h>
using namespace std;
const int maxn = 22;
int n;
char mat[maxn][maxn];
int main() {
    ios_base::sync_with_stdio(false);
    cin >> n;
    vector<int> v;
    for(int i = 0; i < n; i++) {
        v.push_back(i);
        for(int j = 0; j < n; j++) {
            cin >> mat[i][j];
        }
    }
    int res = 2e9;
    
    do {
        int switched = 0;
        for(int i = 0; i < n; i++) {
            for(int j = 0; j < i; j++) {
                if(mat[v[i]][v[j]] == 'D') {
                    switched++;
                }
            }
        }
        res = min(res, switched);
    } while(next_permutation(v.begin(), v.end()));

    cout << res << endl;
    return 0;
}