#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n,ciur[2000005],i,j,counti;
int main()
{
    fin>>n;

    for (i=0;i<=n;i++)
    {
        ciur[i] = 1;
    }

    for (i=2;i*i<=n;i++)
        {
            if (ciur[i]==1)
            {
                for (j=i*i; j<=n;j=j+i)
                    ciur[j] = 0;
            }
        }
        counti=0;
    for(i=2;i<=n;i++)
    {
        if(ciur[i]==1)
        {
            counti++;
        }
    }
    fout<<counti;
    return 0;
}