#include <iostream>

using namespace std;

main()
{
    int n, w, w1=0, w2=1, k=2;

    cin >> n;
    if(n<=1) w=n;
    else
    {
        while(k<=n)
        {
            w=w1+w2;
            w1=w2;
            w2=w;
            k+=1;
        }
    }
    cout << w;

    return 0;
}