rt，3和4WA

#include<bits/stdc++.h>
using namespace std;
int main(){
	long long n,m,hx,hy;
	cin>>n>>m>>hx>>hy;
	n+=2; m+=2; hx+=2; hy+=2;
	unsigned long long a[n+4][m+4]={0};
	for(int i=2;i<=n;i++) a[i][2]=1;
	for(int j=2;j<=m;j++) a[2][j]=1;
	a[hx][hy]=-1;
	a[hx-2][hy-1]=-1;
	a[hx+2][hy-1]=-1;
	a[hx-2][hy+1]=-1;
	a[hx+2][hy+1]=-1;
	a[hx-1][hy-2]=-1;
	a[hx+1][hy-2]=-1;
	a[hx-1][hy+2]=-1;
	a[hx+1][hy+2]=-1;
	for(int i=3;i<=n;i++){
		for(int j=3;j<=m;j++){
			if(a[i][j]!=-1){
				if(a[i-1][j]!=-1){
					if(a[i][j-1]!=-1){
						a[i][j]=a[i-1][j]+a[i][j-1];
					}
					else a[i][j]=a[i-1][j];
				}
				else if(a[i][j-1]!=-1) a[i][j]=a[i][j-1];
				else a[i][j]=0;
			}
		}
	}
	cout<<a[n][m];
	return 0;
} 

3，4点WA