为什么我的程序错了两个点呢？请大佬们看看，谢谢。 源代码：

#include<bits/stdc++.h>
using namespace std;
long long x,y,x2,y2,a[10001][10001]; 
int main()
{
    cin>>x>>y>>x2>>y2;
    for(int i=0;i<=y;i++) a[0][i]=1;
    for(int i=0;i<=x;i++) a[i][0]=1;
	a[x2][y2]=-1;
    if(x2-2>=0&&y2-1>=0) a[x2-2][y2-1]=-1;
	if(x2-2>=0&&y2+1>=0)a[x2-2][y2+1]=-1;
	if(x2+2>=0&&y2-1>=0)a[x2+2][y2-1]=-1;
	if(x2+2>=0&&y2+1>=0)a[x2+2][y2+1]=-1;
	if(x2-1>=0&&y2-2>=0)a[x2-1][y2-2]=-1;
	if(x2+1>=0&&y2-2>=0)a[x2+1][y2-2]=-1;
	if(x2-1>=0&&y2+2>=0)a[x2-1][y2+2]=-1;
	if(x2+1>=0&&y2+2>=0)a[x2+1][y2+2]=-1;
    for(int i=1;i<=x;i++)
    {
    	for(int j=1;j<=y;j++)
    	{
    		if(a[i][j]==-1) continue;
    		if(a[i-1][j]==-1&&a[i][j-1]==-1) a[i][j]=0;
    		else if(a[i-1][j]==-1&&a[i][j-1]!=-1||a[i][j-1]==-1&&a[i-1][j]!=-1) a[i][j]=a[i][j-1]+a[i-1][j]+1;
    		else a[i][j]=a[i][j-1]+a[i-1][j];
		}
	}
	cout<<a[x][y]<<endl;
    return 0;
}