#include <iostream>
#include <fstream>

using namespace std;
int ciur[2000000], c=0;
int main()
{
    ifstream f("ciur.in", ios::in);
    ofstream f2("ciur.out", ios::out    );
    int N;
    f >> N;

    for (long j=4; j<N+1; j+=2){
        ciur[j]=1;

        }
    for (long i=3; i*i<N+1; i+=2)
        if (!ciur[i])
            for (long j=i*i; j<N+1; j+= 2*i) {

                ciur[j] = 1;
            }
    for (long i=2; i<N; ++i)
        if (!ciur[i])
            c++;


    f2 << c;
    return 0;

}