#include <iostream>
#include <fstream>
using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");
int N;
bool p[2000000];

int main()
{
    in>>N;
    for (int i=2;i*i<=N;i++)
        if (!p[i])
            for (int j=i*i;j<=N;j=j+i)
                p[j]=true;
    int nr=0;
    for (int i=2;i<=N;i++)
        if (!p[i])
            nr++;
    out<<nr;
}