hdu 2070 Fibbonacci Number

#include<iostream>
#include<iomanip>
using namespace std;
int main()
{long long a[51]={0,1};for(int i=2;i<51;i++)a[i]=a[i-1]+a[i-2];int n;while(cin>>n&&n!=-1){cout<<a[n]<<endl;}return 0;}