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; Fn+1 = Fn + Fn-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
| 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 }