4.2.17

#include <iostream>
#include <cmath>

using namespace std;

int main()
{
    int n,p=1,p2=1,i=3,Q;
    cin>>n;
    while(i<=n)
    {
        Q=p;
        p=p+p2;
        p2=Q;
        i++;
    }
    if (i>2) cout<<p;
     else cout<<1;
    return 0;
}