#include <bits/stdc++.h>
using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");

bool v[2000005];
int main()
{
    int n,i,j,ct=0;
    in>>n;
    for(i=2;i<=n;i++)
    {
        if(v[i]==0)
        {
            ct++;
            for(j=i+i;j<=n;j=j+i)
                v[j]=1;
        }
    }
    out<<ct;
    return 0;
}