#include <fstream>

using namespace std;

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

void ciur();

int n, nrprime;
bool p[2000005];
int prime[150000];

int main()
{
    fin >> n;
    ciur();
    fout << nrprime;
    return 0;
}

void ciur()
{
    int i, j;

    for (i = 4; i <= n; i+=2)
        p[i] =1;
    for (i = 3; i * i <= n; i+=2)
        if (!p[i])
        {
            for (j = i*i; j <= n; j += i)
                p[j] = 1;
        }
    for (i=2;i<=n;i++)
        if (!p[i])
            prime[++nrprime] = i;
}