C :

#include<stdio.h>
#include<string.h>
int main()
{
	int m,n,x,y,i,j,c[21][21];
	while(scanf("%d%d%d%d",&x,&y,&m,&n)==4)
	{
		memset(c,0,sizeof(c));
		c[m][n]=-1;
		c[0][0]=1;
		if(m>=2&&n>=1)c[m-2][n-1]=-1;
		if(m>=1&&n>=2)c[m-1][n-2]=-1;
		if(y-n>=2&&x-m>=1)c[m+1][n+2]=-1;
		if(y-n>=1&&x-m>=2)c[m+2][n+1]=-1;
		if(m>=2&&y-n>=1)c[m-2][n+1]=-1;
		if(m>=1&&y-n>=1)c[m-1][n+2]=-1;
		if(x-m>=1&&n>=2)c[m+1][n-2]=-1;
		if(x-m>=2&&n>=1)c[m+2][n-1]=-1;
		for(i=1;i<=x;i++)
			if(c[i][0]!=-1)c[i][0]=1;
			else break;
		for(j=1;j<=y;j++)
			if(c[0][j]!=-1)c[0][j]=1;
			else break;
		for(i=1;i<=x;i++)
			for(j=1;j<=y;j++)
				if(c[i][j]!=-1&&c[i][j-1]!=-1&&c[i-1][j]!=-1)
					c[i][j]=c[i][j-1]+c[i-1][j];
				else
				{
					if(c[i][j]!=-1&&c[i][j-1]!=-1)
						c[i][j]=c[i][j-1];
					if(c[i][j]!=-1&&c[i-1][j]!=-1)
						c[i][j]=c[i-1][j];
				}
		printf("%d\n",c[x][y]);
	}
	return 0;
}

C++ :

#include <stdio.h>
#include <string.h>
char a[1000][1000];
int dp[1000][1000];

int main()
{

	int n,m,x,y;
	while(scanf("%d%d%d%d",&n,&m,&x,&y)!=EOF)
	{
		memset(dp,0,sizeof(dp));
		for(int i=0;i<1000;i++)
    	for(int j=0;j<1000;j++)
    	a[i][j]='.';
		n+=2;
		m+=2;
		x+=2;
		y+=2;
		a[x][y]='x';
		a[x-1][y+2]=a[x+1][y+2]=a[x-1][y-2]=a[x+1][y-2]=a[x-2][y+1]=a[x-2][y-1]=a[x+2][y+1]=a[x+2][y-1]='x';
		dp[2][2]=1;
		for(int i=3;i<=m;i++)
		{
			if(a[2][i]!='x')
			dp[2][i]=1;
			if(a[2][i]=='x')
			{
				for(int i1=i;i1<=m;i1++)
				dp[2][i1]=0;
				break;
			}
		}
		for(int i=3;i<=n;i++)
		{
			if(a[i][2]!='x')
			dp[i][2]=1;
			if(a[i][2]=='x')
			{
				for(int i1=i;i1<=n;i1++)
				dp[i1][2]=0;
				break;
			}
		}
	
		for(int i=3;i<=n;i++)
		for(int j=3;j<=m;j++)
		{
			if(a[i][j]=='x')
			dp[i][j]=0;
			else
			dp[i][j]=dp[i-1][j]+dp[i][j-1];
		}

		printf("%d\n",dp[n][m]);
		
	}
	return 0;
}