#include <bits/stdc++.h>
#define nmax 2000007

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

int n;
bool viz[nmax];
int prim[nmax], nr;

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

int main()
{
    fin >> n;
    Ciur();
//    for (int i = 1; i <= nr; i++)
//        fout << prim[i] << " ";
    fout << nr;
    fout << "\n";
    return 0;
}