CHONQUA C++

#include <bits/stdc++.h>
using namespace std;
int m,n,k,a[1005][1005],f[1005][1005];

void nhap()
{
    char x;
    cin>>m>>n>>k;
    for (int i=1;i<=m;i++){
        for (int j=1;j<=n;j++) {
            cin>>x;
          //  cout<<x;
            if(x=='.') a[i][j]=0;
            else a[i][j]=1;
        }
    }
   /*  for(int i=1;i<=m;i++){
        for(int j=1;j<=n;j++){
            cout<<a[i][j]<<" ";
        }
        cout<<endl;
    }*/
}

void taof()
{
    for (int i=1;i<=m;i++)
        for (int j=1;j<=n;j++)
		f[i][j]=f[i-1][j]+f[i][j-1]-f[i-1][j-1]+a[i][j];
}

void xuli()
{
    long long maxx=0,s=0;
    int x1,x2,y1,y2;
    k=k-2;
 //   cout<<k<<endl;
    for (int x1=2;x1<=m-k;x1++)
    {
        for (int y1=2;y1<=n-k;y1++)
        {
            x2=x1+k-1;
            y2=y1+k-1;
            s=f[x2][y2]-f[x1-1][y2]-f[x2][y1-1]+f[x1-1][y1-1];
            if (maxx<s) maxx=s;
        }
    }
    cout<<maxx;
}

int main()
{
     ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
   // freopen("b.inp","r",stdin);
   // freopen("b.out","w",stdout);
    nhap();

    taof();
    xuli();
}