#include <iostream>
#include <fstream>

using namespace std;

#define NMax 2000000
ifstream f("ciur.in");
ofstream g("ciur.out");

int n;
char ciur[NMax];

int main()
{
    int i, j, nr = 0;

    f >> n;

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

    for(i = 2; i <= n; i++)
        if(ciur[i] == 0)
            nr++;

    g << nr;
    return 0;
}