count reachable

#include <bits/stdc++.h>
using namespace std;
// count reachable
const int N = 100;
char a[N][N];
int n, m;
bool vis[N][N];
bool valid (int row, int col) {
    return (row >= 0 && col >= 0 && row < n && col < m);
}
int cnt;
void count (int row, int col) {
    // base case
    if (!valid(row, col) || a[row][col] == 'X' || vis[row][col])
        return;
    // recursive case
    vis[row][col] = true;
    cnt++;
    count(row + 1, col);
    count(row - 1, col);
    count(row, col + 1);
    count(row, col - 1);
}
int main () {
//    freopen("/home/hamoudi/clion/hello.in", "rt", stdin);
    cnt = 0;
    cin >> n >> m;
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < m; ++j) {
            cin >> a[i][j];
        }
    }
    count(0, 0);
    cout << cnt << '\n';
}