#include <iostream>
#include <fstream>

using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");

bool a[2000005];
int main()
{
    int n,contor=1,k;
    f>>n;
    for(int i=3;i<=n;i=i+2) a[i]=1;
    k=3;
    while(k<=n)
    {
        if(a[k]==1)
        {
            contor++;
            for(int i=k;i<=n;i=i+k) a[i]=0;
        }
        k=k+2;
    }
    g<<contor<<'\n';
    return 0;
}