sgu 123 The sum

#include <stdio.h>#include <string.h>#include <math.h>using namespace std;int f[50];int main(){    int i,n;    f[1]=f[2]=1;    for(i=3;i<=40;i++)        f[i]=f[i-1]+f[i-2];    while(scanf("%d",&n)!=EOF)    {        int s=0;        for(i=1;i<=n;i++)            s+=f[i];        printf("%d\n",s);    }    return 0;}