#include <iostream>
using namespace std;
int main()
{
    int n=3;
    while(printf("n(n>=3):")&&cin>>n)
    {
        int a1=1,a2=1,a3=2;
        int i;
        for(i=3;i<=n;i++)
        {
            a3=a1+a2;
            a1=a2;
            a2=a3;
        }
        cout<<a3<<endl;
    }
    return 0;
}