代码如下qwq：

#include <iostream>
#include <algorithm>
using namespace std;
int n, m, a[1005][1005], x, y;
int main(){
	cin >> n >> m;
	for(int i = 1; i <= m; i++){
		cin >> x >> y;
		a[x][y] = -1;
	}
	a[1][1] = 1;
	for(int i = 1; i <= n; i++){
		for(int j = 1; j <= n; j++){
			if(a[i][j] == -1) continue;
			if(i == 1 && j == 1) continue;
			if(a[i - 1][j] != -1) a[i][j] += a[i - 1][j];
			if(a[i][j - 1] != -1) a[i][j] += a[i][j - 1];
		}
	}
	cout << a[n][n] << endl;
	return 0;
}