#include<iostream>
#include<fstream>
#include<stdio.h>
#include<vector>
using namespace std;
char v[2000005];
int main()
{int  k,n;
long long  j,i;
ifstream fin("ciur.in");
  fin>>n;
  k=0;
  v[1]=v[0]=1;
  for(i=2;i<=n;i++)
    if(v[i]==0)
    {k++;
    for(j=i*i;j<=n;j+=i)
       {v[j]=1;
       }
    }

fin.close();
  freopen("ciur.out","w",stdout);
    printf("%d \n",k);


    return 0;
}