#include<bits/stdc++.h>
using namespace std;
typedef long double ll;
string arr[707];
ll PI = 3.1415926535879;
ll dp[1500][750];
ll cn = PI * 2.5;
int main() {
 int n, m, i, j, k, b, c;
 ll a;
 cin >> n >> m;
 for ( i = 0; i < n; i++ ) {
  cin >> arr[i];
 }
 for ( i = 0; i <= 2 * n; i++ ) {
  if ( i % 2 == 0 ) {
   for ( j = 0; j < m; j++ ) {
    if ( i == 0 && j == 0 )dp[i][j] = 0.0;
    else {
     dp[i][j] = -1;
     if ( j > 0 )dp[i][j] = dp[i][j - 1] + 10.0;
     if ( i > 0 ) {
      a = cn;
      if ( arr[i / 2 - 1][j] == 'X' )a = 10.0;
      if ( dp[i][j] == -1 || dp[i][j] > dp[i - 1][j] + a )dp[i][j] = dp[i - 1][j] + a;
     }
    }
   }
  } else {
   for ( j = 0; j <= m; j++ ) {
    if ( i == 1 && j == 0 ) {
     dp[i][j] = 0.0;
    } else {
     dp[i][j] = -1;
     if ( i > 1 )dp[i][j] = dp[i - 2][j] + 10.0;
     if ( j > 0 ) {
      a = cn;
      if ( arr[i / 2][j - 1] == 'X' )a = 10.0;
      if ( dp[i][j] == -1 || dp[i][j] > dp[i - 1][j - 1] + a )dp[i][j] = dp[i - 1][j - 1] + a;
     }
    }
   }
  }
 }
 cout << fixed << setprecision(7) << min(dp[2 * n][m - 1], dp[2 * n - 1][m]) + 10.0;
}