/******************************************************************************
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*******************************************************************************/
#include <stdio.h>
#include <iostream>
#include <cmath>
using namespace std;
int F(int n){
if( n <= 1){
return n;
}
return F(n - 2) + F(n - 1);
}
int main(){
int n;
cin >> n;
cout << F(n);
return 0;
}