#include <iostream>
#include <fstream>
#include <cstring>

using namespace std;

ifstream in("ciur.in");
ofstream out("ciur.out");

bool v[1000001];

int main()
{
    int n;
    in>>n;

    //bool v[n+1];
v[0]=1;
v[1]=1;
    for (int i=2;i * i<=n;i++)
    {
        if (!v[i])
           {
        for (int j=i * i;j<=n;j+=i)
                v[j]=true;
           }
    }
    int c=0;
    for (int i=1;i<=n;i++)
        if (!v[i])
            c++;

        out<<c;
}