For binomial coefficients (the number of combinations from n to k), the recurrent formula is well known:
\(C^k_n=C^{k-1}_{n-1}+C^ {k}_{n-1}\),
\(C^0_n = C^n_n=1\).
Input
Enter 2 numbers - n and k.
Imprint
You need to output value
\(С^k_n\) .
Examples