#include <iostream>
#include <cstring>
using namespace std;
char mat[22][22];
int n;
int dp[1 << 21];

int rec(int bitmask) {
    if(__builtin_popcount(bitmask) == n ) {

        return 0;
    }
    if(dp[bitmask] != -1) {
        return dp[bitmask];
    }
    int res = 2e9;
    for(int i = 0; i < n; i++) {
        if(bitmask & (1 << i)) continue;
        int c = 0;
        for(int j = 0; j < n; j++) {
            if(bitmask & (1 << j)) {
                if(mat[i][j] == 'D') {
                    c++;
                }
            }
        }
        res = min(res, rec(bitmask | (1 << i)) + c);
    }
    return dp[bitmask] = res;
}
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];
        }
    }
    memset(dp, -1, sizeof dp);
    cout << rec(0) << endl;
    return 0;
}