#include <iostream>
#include <cmath>

using namespace std;

int main(int argc, char** argv)
{

int n;
int f[45];

while(cin>> n)
{
f[0]=1;
f[1]=2;
for (int i=2;i<=n-1;i++)
{
f[i]=f[i-1]+f[i-2];
}

cout << f[n-1] << endl;
}





return 0;
}