#include <iostream>
using namespace std;
int d[20] = {0};
int fibo(int n){
if(d[n-1]){
return d[n-1];
}
else{
return d[n-1] = fibo(n-1)+fibo(n-2);
}
}
int main(){
int n;
cin >> n;
d[0] = 1;
d[1] = 2;
cout << fibo(n);
}