60分求助大佬

#include <iostream>
#include <cstring> 

using namespace std;

int m, n, x, y;
long long N[25][25];



int main()
{
	for (int i = 0; i < 21; ++i) {
    	for (int j = 0; j < 21; ++j) {
        	N[i][j] = 1;
    	}
	}
	
	cin >> n >> m >> x >> y;
	
	
	for (int i=0;i<21;i++)
	{
		N[i][0] = 1;
		N[0][i] = 1;
	}
	
	N[x][y] = 0;
	if(x-1>=0&&y-2>=0){N[x-1][y-2]=0;}
	if (y-2>=0){N[x+1][y-2]=0;}
	if(y-1>=0){N[x+2][y-1]=0;}
	N[x+2][y+1]=0;
	N[x+1][y+2]=0;
	if(x-1>=0){N[x-1][y+2]=0;}
	if(x-2>=0){N[x-2][y+1]=0;}
	if(x-2>=0&&y-1>=0){N[x-2][y-1]=0;}
	

	
	for (int i=1;i<=n;i++)
	{
		for (int j=1;j<=m;j++)
		{
			if (N[i][j]!=0)
			{
//				cout << "in";
				N[i][j] = N[i][j-1]+N[i-1][j];
			}
			
		}
		
	}
	

//	
//	for (int i=0;i<=n;i++)
//	{
//		for (int j=0;j<=m;j++)
//		{
//			cout << N[i][j] << " ";
//			
//		}
//		cout << endl;
//	}

////	
	cout << N[n][m];
	
	return 0;
 }