#include <bits/stdc++.h>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

bitset <2000005>a;
int n, s;

void Citire()
{
    fin >> n;
}

void Ciur()
{
    int i, j;

    a[1] = 1;
    for(i = 4; i <= n; i += 2)
        a[i] = 1;

    for(i = 3; i * i <= n; i += 2)
        if(a[i] == 0)
        for(j = i * i; j <= n; j = 2 * i + j)
            a[i] = 1;

    for(i = 1; i <= n; i++)
        if(a[i] == 0)
            s++;
    fout << s << "\n";
}
int main()
{
    Citire();
    Ciur();
    return 0;
}