Project Euler 015

#include 
using namespace std;
#define int long long
const int N = 25;
int f[N][N];

signed main () {
	for(int i = 1;i <= 21; i ++) {
		for(int j = 1;j <= 21; j ++) {
			if(i == 1 or j == 1) f[i][j] = 1;
			else f[i][j] = f[i - 1][j] + f[i][j - 1];
		}
	}
	cout << f[21][21] << endl;
	return 0;
}