#include <iostream>
#include<fstream>
using namespace std;
ifstream in ("ciur.in")
ofstream out ("ciur.out")
int main()
{
    long long N,i,s=0,j;
    in>>N;
    bool sir[2000001];
    sir[1]=1;
    for(i=2;i<=N;i++)
    {
        if(sir[i]==0)
        {
            s=s+1;
            if(i*i<=N)
            {
                for(j=i+i;j<=N;j=j+i)
                sir[j]=1;
            }
        }
    }
    out<<s;
    return 0;
}