#include<cstdio>
#include<iostream>
#pragma GCC optimize(3)
using namespace std;
int a[50];
int f(int n)
{
if(n == 0 || a[n]) return a[n];
a[n] = f(n - 1) + f(n - 2);
return a[n];
}
int main(void)
{
a[1] = 1;
int n;
scanf("%d", &n);
printf("%d\n", f(n));;
return 0;
}