60pts求助

#include<iostream>
using namespace std;
int a[1005][1005];
int main(){
    int n,m,k,x,y,o,p,s=0;
    cin>>n>>m>>k;
    for(int i=1; i<=m; i++){
    	cin>>x>>y;
    	a[x][y]=1;
    	a[x+1][y]=1;
    	a[x+1][y+1]=1;
    	a[x][y-1]=1;
    	a[x-1][y]=1;
    	a[x-1][y-1]=1;
    	a[x-1][y+1]=1;
    	a[x+1][y-1]=1;
    	a[x][y+1]=1;
    	a[x][y+2]=1;
    	a[x][y-2]=1;
    	a[x+2][y]=1;
    	a[x-2][y]=1;
    }
    for(int i=1; i<=k; i++){
    	cin>>o>>p;
    	a[o][p]=1;
    	a[o+1][p]=1;
    	a[o+1][p+1]=1;
    	a[o][p-1]=1;
    	a[o-1][p]=1;
    	a[o-1][p-1]=1;
    	a[o-1][p+1]=1;
    	a[o+1][p-1]=1;
    	a[o][p+1]=1;
    	
    	a[o+2][p]=1;
    	a[o+2][p+2]=1;
    	a[o][p-2]=1;
    	a[o-2][p]=1;
    	a[o-2][p-2]=1;
    	a[o-2][p+2]=1;
    	a[o+2][p-2]=1;
    	a[o][p+2]=1;
    	
    	a[o+2][p-1]=1;
    	a[o+2][p+1]=1;
    	a[o-2][p-1]=1;
    	a[o-2][p+1]=1;
    	a[o+1][p-2]=1;
    	a[o+1][p+2]=1;
    	a[o-1][p+2]=1;
    	a[o-1][p-2]=1;
    }
    for(int i=1; i<=n; i++){
    	for(int j=1; j<=n; j++){
    	   if(a[i][j]==0){
    	   	  s++;
    	   }
    	}
    }
    cout<<s;
    return 0;
}