include <iostream>
include <stdlib.h>
include <stdio.h>
include <string.h>
include <math.h>
using namespace std;
int x;
int f(int n){
if (n <= 2){
x = n;
}
else{
x = f(n-1) + f(n-2); //递归
}
return x;
}
int main(){
int N;
cin >> N;
cout << f(N);
return 0;
}
