#include<bits/stdc++.h>
using namespace std;
ifstream fcin("ciur.in");
ofstream fcout("ciur.out");


const int N = 2e6 + 5;
bitset<N> p;

void ciur(int n)
{
    p[2] = 1;
    for (int i = 3; i <= n; i += 2)
        p[i] = 1;
    for (int i = 3; i <= n; i += 2)
        if (p[i])
            for (int j = i * i; j <= n; j += 2 * i)
                p[j] = 0;
}

int main()
{
    int n, r;
    fcin >> n;
    ciur(n);
    r = 0;
    for (int i = 2; i <= n; i++)
    {
        r += p[i];
    }
    fcout << r;


    return 0;
}