DFS

#include "bits/stdc++.h"
using namespace std;
char arr[21][21];
int n,m;
int dfs(int x,int y)
{
    if(x<1||x>n||y<1||y>m)
        return 0;
    if(arr[x][y]=='#')
        return 0;
    arr[x][y]='#';
    return 1+dfs(x-1,y)+dfs(x+1,y)+dfs(x,y-1)+dfs(x,y+1);
}
int main()
{
    cin>>m>>n;
    int x,y;
    for(int i=1;i<=n;i++)
        for(int j=1;j<=m;j++)
        {
            cin>>arr[i][j];
            if(arr[i][j]=='@')
            {
                x=i;
                y=j;
            }
        }
    cout<<dfs(x,y)<<endl;
    return 0;
}