Polynomial coefficients

The problem is to calculate the coefficients in expansion of polynomial (x1 + x2 + . . . + xk)n. Input The input will consist of a set of pairs of lines. The first line of the pair consists of two integers n and k separated with space (0 < K,N < 13). This integers define the power of the polynomial and the amount of the variables. The second line in each pair consists of k non-negative integers n1,...,nk, where n1 + . . . + nk = n. Output For each input pair of lines the output line should consist one integer, the coefficient by the monomial xn1xn2 ...xnk in expansion of the polynomial (x1 +x2 +...+xk)n. 12k Sample Input 22 11 2 12 100000000010 Sample Output 2 2