#include <bits/stdc++.h>
#define MOD 1000000007
using namespace std;

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

int n, p[2000003];

void Ciur(int n)
{
    int i, j;
    for (i = 4; i <= n; i += 2)
        p[i] = 1;
    for (i = 3; i * i <= n; i += 2)
        if (p[i] == 0)
            for (j = i * i; j <= n; j += 2 * i)
                p[j] = 1;
}

int main()
{
    int i, cnt = 0;
    fin >> n;
    Ciur(n + 1);
    for (i = 2; i <= n; i++)
        if (p[i] == 0) cnt++;
    fout << cnt << '\n';
    fout.close();
    return 0;
}