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