#!/usr/bin/env python3
import math

h, w = map(int, input().split())

b = [input() for _ in range(h)]

dp = [[0] * (2 * w + 1) for _ in range(2 * h + 1)]
for i in range(1, 2 * h + 1):
    for j in range(1, 2 * w + 1):
        if (i + j) % 2 == 0:
            continue
        if i % 2 == 0:
            dp[i][j] = max(
                dp[i][j - 2], dp[i - 1][j - 1] + (b[i // 2 - 1][j // 2] == "O")
            )
        else:
            dp[i][j] = max(
                dp[i - 2][j], dp[i - 1][j - 1] + (b[i // 2][j // 2 - 1] == "O")
            )
print(10*((w + h) - (max(dp[-1][-2], dp[-2][-1])) * (1 - math.pi / 4)))