SGU123 - The sum

123. The sum

time limit per test: 0.5 sec. 
memory limit per test: 4096 KB

 

The Fibonacci sequence of numbers is known: F₁ = 1; F₂ = 1; F_n+1 = F_n + F_n-1, for n>1. You have to find S - the sum of the first K Fibonacci numbers.

 

Input

First line contains natural number K (0<K<41).

 

Output

First line should contain number S.

 

Sample Input

5

 

Sample Output

12

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Author	: Paul "Stingray" Komkoff, Victor G. Samoilov
Resource	: 5th Southern Subregional Contest. Saratov 2002
Date	: 2002-10-10

 

 

 

题解：迭代一下就行。。。数组都不用开。。。

View Code

 1 #include<stdio.h>

 2 int main(void)

 3 {

 4     long f1,f2,f3,k,i;

 5     long long ans;

 6     scanf("%ld",&k);

 7     if(k==1)

 8     {

 9         printf("1\n");

10         return 0;

11     }

12     ans=2;

13     i=3;

14     f1=1;

15     f2=1;

16     while(i<=k)

17     {

18         f3=f1+f2;

19         ans+=f3;

20         f1=f2;

21         f2=f3;

22         i++;

23 

24     }

25     printf("%lld\n",ans);

26     return 0;

27 }