#include <bits/stdc++.h>
#define newline '\n'
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
///***********************
const int NMAX = 2e6 + 3;
bool prime[NMAX];
int n;

void initSieve()
{
    memset(prime, true, sizeof(prime));
    prime[1] = false;
    for (int i = 2; i * i <= n; i++)
        if (prime[i])
        {
            for (int j = i * i; j <= n; j += i)
                prime[j] = false;
        }
}

int main()
{
    fin >> n;
    initSieve();
    #define prime prime + 1
    fout << count_if(prime, prime + n, [](bool e)
    {
        return e;
    });
    return 0;
}