Rumus C++ Menentukan Bilangan Fibonacci

#include <iostream>
using namespace std;
int main(){
   int a1=1,i=1,a2=2,a3,akhir;
    cout<<"Masukan Nilai Batas Fibonacci : "; cin>>akhir;
    cout<<endl<<"Program menghitung Deret Fibonaci sampai suku ke-"<<akhir <<endl<<endl;
    cout<<a1<<","<<a2<<",";
        while(!(i>(akhir-2))){
            a3=a1+a2;
                cout<< a3 <<",";
            a1=a2;
            a2=a3;
            i =i+1;
        }
    cout<<endl<<endl;
   return 0;
}