#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>
#define NMAX 2000005
using namespace std;
ifstream fin ("ciur.in");
ofstream fout ("ciur.out");
int n,c;
bool v[NMAX];
int main()
{
    fin >> n;
    for(int i=2;i<=n;++i)
    {
        v[i]=true;
    }
    for(int i=2;i*i<=n;++i)
    {
        if(v[i])
        {

            for(int j=i*i;j<=n;j+=i)
                v[j]=false;
        }
    }
    for(int i =2;i<=n;++i)
        if(v[i])
             c++;
    fout << c;
    return 0;
}