table = [[-1 for i in range (0,50)] for i in range(0, 50)] //Create a 50*50 table with -1 in each cell
def nCr(n, r):
    if r==1: return n
    if n==r: return 1
    if table[n][r] != -1:
        return table[n][r]
    table[n][r] = nCr(n-1, r) + nCr(n-1, r-1)
    return table[n][r]