老师写的。

#include<bits/stdc++.h>
using namespace std;

int a[25][25];
unsigned long long dp[25][25];

int main() {
    int p, q, mx, my;
    scanf("%d %d %d %d", &p, &q, &mx, &my);
	p++, q++, mx++, my++;
    a[mx][my] = 5;
    a[mx - 2][my - 1] = 5;
    a[mx - 2][my + 1] = 5;
    a[mx - 1][my - 2] = 5;
    a[mx - 1][my + 2] = 5;
    a[mx + 1][my - 2] = 5;
    a[mx + 1][my + 2] = 5;
    a[mx + 2][my - 1] = 5;
    a[mx + 2][my + 1] = 5;
    dp[1][1] = 1;
	for(int i = 1; i <= p; i++) {
		for(int j = 1; j <= q; j++) {
			if(a[i][j] == 5) {
				continue;
			}
            dp[i][j] = max(dp[i][j], dp[i - 1][j] + dp[i][j - 1]);
		}
	}
    printf("%llu\n", dp[p][q]);
	return 0;
}