快速切题 sgu123. The sum
123. The sum
time limit per test: 0.25 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
#include <cstdio> #include <cstring> using namespace std; const int maxn=41; long long f[maxn]; int main(){ int k;long long s=1; scanf("%d",&k);f[1]=1; for(int i=2;i<=k;i++){ f[i]=f[i-1]+f[i-2]; s+=f[i]; } printf("%I64d\n",s); return 0; }