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#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 dp[1 << maxn];
int bits_i[maxn];
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 switched = __builtin_popcount(bitmask & bits_i[i]);
        
        res = min(res, rec(bitmask | (1 << i)) + switched);
    }
    return dp[bitmask] = res;
}
string to_string_bit(int x) {
    string s = "";
    while(x > 0) {
        s += (x % 2) + '0';
        x /= 2;
    }
    reverse(s.begin(), s.end());
    return s;
}
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 num = 0;
        for(int j = n - 1; j >= 0; j--) {
            if(mat[i][j] == 'D') {
                num |= (1 << j);
            }
        }
        bits_i[i] = num;
    }
   
    fill(dp, dp + (1 << maxn), -1);
    cout << rec(0) << endl;
    return 0;
}