#include <iostream>
#include <fstream>
#include <math.h>
using namespace std;
bool npr[2000001];
int n,cnt,i,j,x;
ifstream f("ciur.in");
ofstream g("ciur.out");
int main()
{
    f>>n;
    cnt=n/2;
    x=sqrt(n);
    for(i=3;i<=x;i+=2)
        if(!npr[i])
            for(j=3*i;j<=n;j+=i*2)
                npr[j]=true,cnt++;
    g<<n-cnt;
    return 0;
}