#include <iostream>
#include <cstdio>
#include <bitset>
#include <fstream>

using namespace std;
long long n,z;
bitset <3000000> a;
ifstream f("ciur.in");
ofstream g("ciur.out");

int main()
{
    f >> n;
    z++;
    for(long long i=3; i<=n; i+=2){
        if(a[i] == 0)
            z++;
        for(long long j=i*i; j<=n; j+=2*i)
            a[j] = 1;
    }
    g << z << endl;
}