代码如下```

#include<iostream>
#include<vector>
using namespace std;
int main(){
int x1,y1,x2,y2;
cin>>x1>>y1>>x2>>y2;
vector<vector<int>>dp(x1+1,vector<int>(y1+1,0));
for(int i=0;i<=x1;i++)dp[i][0]=1;
for(int j=0;j<=y1;j++)dp[0][j]=1;
if (x2 + 2 <= x1 && y2 + 1 <= y1) dp[x2 + 2][y2 + 1] = 0; 
if (x2 + 2 <= x1) dp[x2 + 2][y2] = 0; 
if (x2 + 1 <= x1 && y2 - 2 >= 0) dp[x2 + 1][y2 - 2] = 0;
for(int i=1;i<=x1;i++){
for(int j=1;j<=y1;j++){
if(dp[i][j]!=0){
dp[i][j]=dp[i-1][j]+dp[i][j-1];
}
}
}
cout<<dp[x1][y1];
}