#include <bits/stdc++.h>
#define ri register
#define int long long
#define E (n+1)
using namespace std; const int N=200010;
inline int read()
{
    int s=0, w=1; ri char ch=getchar();
    while(ch<'0'||ch>'9') { if(ch=='-') w=-1; ch=getchar(); }
    while(ch>='0'&&ch<='9') s=(s<<3)+(s<<1)+(ch^48), ch=getchar();
    return s*w;
}
signed main()
{
    int n=read();
    printf("%lld\n",n/3);
    return 0;
}
#include<iostream>
using namespace std;
int main()
{
  int n;
  cin >> n;
  if(n / 3. >= 1)
    cout << n / 3;
  else cout << 0;
  return 0;
}
