#include<cstdio>
#include<iostream>
using namespace std;
int main()
{
int f[100];
f[0] = 0, f[1] = 1;
int n;
cin >> n;
for (int i = 2; i <= n; i++)
{
f[i] = f[i - 1] + f[i - 2];
}
cout << f[n] << endl;
return 0;
}