파스칼 삼각형(조합)

nCr = n-1Cr-1 + n-1Cr

 

n, r = map(int, input().split())
dp = [[1]*(i+1) for i in range(n+1)]

for i in range(2, n+1):
    for j in range(1, i):
        dp[i][j] = dp[i-1][j-1]+dp[i-1][j]

print(dp[n][r])  # nCr