#include<iostream>
using namespace std;
long long count=0;

void resolve(int begin,int end){
    if(begin == end){
        count++; 
        return;
    }
    if(begin+1<=end){
        resolve(begin+1,end);
    }
    if(begin+2<=end){
        resolve(begin+2,end);
    }
}
int main(){
    int n;
    cin>>n;
    resolve(0,n);
    cout<<count<<endl;
    return 0;
}