#define io ios_base::sync_with_stdio(false);cin.tie(NULL);cin.tie(nullptr), cout.tie(nullptr);

#include <bits/stdc++.h>

#define ll long long
#define double long double
using namespace std;

const int N = 705;

int n, m;
char arr[N][N];
double dp[N][N][4];
// 1 -> right to me
// 2 -> down

vector<vector<double>> fromTo[3] = {
        {{1, 5, 0}, {2, 5,                 0}},
        {{0, 5, 1}, {2, 10 * acos(-1) / 4, 1}},
        {{0, 5, 2}, {1, 10 * acos(-1) / 4, 2}},
};

double solve(int x, int y, int edge) {
    if (x == n && y == m && !edge) {
        return 0;
    }
    if (x > n || y > m)return 1e9;
    double &ret = dp[x][y][edge];
    if (ret != -1)return ret;
    ret = 1e9;
    if (arr[x][y] == 'X') {
        if (!edge)
            ret = min(solve(x + 1, y, 0), solve(x, y + 1, 0)) + 10;
        else if (edge == 1)
            ret = solve(x, y + 1, 0) + 5;
        else if (edge == 2)
            ret = solve(x + 1, y, 0) + 5;
    } else {
        for (auto i: fromTo[edge]) {
            ret = min(ret, solve(x + (i[2] == 2), y + (i[2] == 1), i[0]) + i[1]);
        }
    }
    return ret;
}

void solve() {
    cin >> n >> m;
    for (int i = 0; i <= n; ++i) {
        for (int j = 0; j <= m; ++j) {
            for (int k = 0; k < 4; ++k) {
                dp[i][j][k] = -1;
            }
        }
    }
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < m; ++j) {
            cin >> arr[i][j];
        }
    }
    for (int i = 0; i <= m; ++i) {
        arr[n][i] = 'X';
    }
    for (int i = 0; i <= n; ++i) {
        arr[i][m] = 'X';
    }
    cout << setprecision(8) << solve(0, 0, 0);
}

signed main() {
    io
    int t;
    t = 1;
//    cin >> t;
    while (t--) {
        solve();
    }
}