#include <iostream>
#include <fstream>
using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");
int n,i,k,j;
char v[2000001];
int main()
{
    v[0]='1';
    v[1]='1';
    for(i=2;i*i<2000000;i++)
    {
        if (v[i]==0)for(j=i+i;j<=2000000;j=j+i)v[j]='1';
    }
    in>>n;
    for(i=1;i<=n;i++)
    {
        if(v[i]==0)k++;
    }
    out<<k;
    return 0;
}