#include <iostream>
#include <fstream>
using namespace std;
int n;
bool v[2000001];
int i,j;
int s;
int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f>>n;
    v[0]=v[1]=false;
    for(i=2;i<=n/2;i++)
    {
        if(v[i]==false)
            for(j=2*i;j<=n;j+=i)v[j]=true;
    }
    for(j=2;j<=n;j++)
    {
        if(v[j]==false)s++;
    }
    g<<s;
}