#include <iostream>
#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
int n,i,j,v[2000002],k;
int main()
{
    in>>n;
    k=0;
    for(i=2;i<=n;i++) v[i]=1;

    for(i=2;i<=n;i++)
    {
        if(v[i]==1)
        {
            k++;
            for(j=i+i;j<=n;j=j+i)
                v[j]=0;
        }
    }
    out<<k;
    return 0;
}