#include<iostream>
using namespace std;

int main() {
    long long a[53]={0};
    int n;
    
    cin >> n;
    a[0]=1;
    for (int i=0;i<=n;i++) {
        a[i+1]+=a[i]; a[i+2]+=a[i];
    }
    cout << a[n] << endl;
    return 0;
}