#include<iostream>
#include<fstream>
using namespace std;
bool v[2000002];
int main ()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    int i,n,j,s=1;
    f>>n;
    for(i=3;i<=n/2;i+=2)
    {
        if(v[i]==0)
        {
        for(j=i*i;j<=n;j+=i)
            v[j]=1;
        }
    }
    for(i=3;i<=n;i+=2)
       if(v[i]==0)
            s++;
    g<<s;
}