#include<cstdio>
#include<iostream>
#include <algorithm>
using namespace std;
long long n;
long long cnt=0;
int vis[1005];
void dfs(int cur,int res)
{
    if(res>=cur)
    {
        cnt++;
        return ;
    }
    if(vis[res]==0)
    {
        vis[res]=1;
        dfs(cur,res+1);
        dfs(cur,res+2);
    }
}
int main()
{
    cin>>n;
    dfs(n,1);
    cout<<cnt;
}