#include <fstream>

using namespace std;
ifstream inputfile("ciur.in");
ofstream outputfile("ciur.out");

bool prime[2000001];
long number, index1, index2, solutions;

int main() {

    inputfile >> number;
    for (index1 = 1; index1 <= number; index1++)
        prime[index1] = true;

    for ( index1 = 2; index1 * index1 <= number; index1++)
    {
        if(prime[index1])
        {
            //solutions++;
            for (index2 = 2 * index1; index2 <= number; index2 += index1)
                prime[index2] = false;
        }
    }
    for(index1 = 2; index1 <= number ; index1++)
        if (prime[index1]) solutions++;
    outputfile << solutions;
    return 0;
}