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;
}