0046. Sum of Products
| Имя входного файла: | sumprod.in |
| Имя выходного файла: | sumprod.out |
| Ограничение по времени: | 1 s |
| Ограничение по памяти: | 64 megabytes |
Of course you know that there are Ckn ways to select k numbers from a set of n. Given a set of n integer numbers, Anton for each such combination calculates its total product and then sums all products.
For example, if the numbers are (2, 2, 3), k=2 and n=3 he will get 2⋅ 2+2⋅ 3+2⋅ 3=16.
Your task is to calculate the answer he will get.
Input file
The first line of the input file contains two integer numbers n and k (1≤ k≤ n≤ 200). The second one contains n non-negative integer numbers. These numbers will not be greater than 32000.
Output file
Output only one integer number – sum of all products by k.
Examples:
| sumprod.in | sumprod.out |
|---|---|
| 3 2 2 2 3 | 16 |
Источник: Petrozavodsk training camp, Summer 2002. Conclusive contest
Автор: Andrew Lopatin, Nick Durov
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