#include <iostream>
#include <fstream>

using namespace std;

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

bool f[2000001];
int n, c;

void eras()
{
    f[2]=1, c++;
    for(int i=3; i<=n; i+=2) f[i]=1;
    for(int i=3; i<=n; i+=2)
    {
        if(f[i]==1)
        {
            c++;
            for(int j=i*2; j<=n; j+=i) f[j]=0;
        }
    }
}

int main()
{
    in>>n;
    eras();
    out<<c;
    return 0;
}