1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
#include <bits/stdc++.h>
using namespace std;

char start[20][20], finish[20][20];

long long binom(int a, int b) {
	if (b < 0 || a < b) {
		return 0ll;
	}
	
	long long result = 1;
	for (long long i = a - b + 1; i <= a; i++) {
		result *= i;
	}
	for (long long i = 2; i <= b; i++) {
		result /= i;
	}
	return result;
}

int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(nullptr);
	
	int n, m;
	cin >> n >> m;
	
	for (int row = 0; row < n; row++) {
		cin >> start[row];
	}
	for (int row = 0; row < n; row++) {
		cin >> finish[row];
	}
	
	int k = 0;
	int start_parity = 0;
	for (int row = 0; row < n; row++) {
		for (int column = 0; column < m; column++) {
			if (start[row][column] == 'O') {
				k++;
				start_parity ^= row;
				start_parity ^= column;
			}
		}
	}
	start_parity &= 1;
	
	long long numerator = 0, denominator = 0;
	int finish_parity = 0;
	for (int row = 0; row < n; row++) {
		for (int column = 0; column < m; column++) {
			if (finish[row][column] == 'O') {
				finish_parity ^= row;
				finish_parity ^= column;
				
				if (row > 0 && finish[row - 1][column] != 'O') {
					numerator++;
				}
				if (row < n - 1 && finish[row + 1][column] != 'O') {
					numerator++;
				}
				if (column > 0 && finish[row][column - 1] != 'O') {
					numerator++;
				}
				if (column < m - 1 && finish[row][column + 1] != 'O') {
					numerator++;
				}
			}
		}
	}
	finish_parity &= 1;
	
	if (start_parity != finish_parity) {
		cout << fixed << setprecision(16) << 0.0 << '\n';
		return 0;
	}
	
	denominator = binom(n * m - 2, k - 1) * (m * (n - 1) + n * (m - 1));
	
	cout << fixed << setprecision(16) << (long double) numerator / denominator << '\n';
	
	return 0;
}