#include <iostream>
#include <fstream>
using namespace std;
int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    long long i,j,N,contor=0;
    bool a[2000005];
    for (i=2;i<=2000000;++i)
    {
        a[i]=1;
    }
    a[1]=0;
    for (i=2;i<=2000000;i++)
    {
        if (a[i]==1)
        {
            for (j=i*i;j<=2000000;j=j+i)
            {
                a[j]=0;
            }
        }
    }
    fin >> N;
    for (i=2;i<=N;++i)
    {
        if (a[i])
        {
            ++contor;
        }
    }
    fout << contor;
    return 0;
}