Sgu-123-the sum (simple math!) ）

SGU-123The sum Time Limit: 250MS Memory Limit: 4096KB 64bit IO Format: %i64d &%i64u Submit Status Description Here is your second problem, keep calm and solve it. Nacci sequence of numbers is known to all: F1 = 1; F2 = 1; fn+1 = fn + Fn-1, for n>1. You have to find S -The sum of the first K nacci numbers. Input First line contains natural number K (0<k<41) . Output First line should contain number S. Sample Input 5 Sample Output 12 Source

Simple math sum problem,, incredibly int will not explode, at first I thought to long long.

AC Code:

Sgu-123-the sum (simple math!) ）