#include <iostream>
#include <fstream>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");
bool erath[2000005];
int main()
{
    erath[0]=1;erath[1]=1;
    int n;
    int prime=0;
    fin>>n;
    for(int div=2; div*div<=n; div++)
    {
        if(erath[div]==1)
            continue;
        for(int mul=2*div; mul<=n; mul+=div){
            erath[mul]=1;
        }
    }
    for(int i=1; i<=n; i++)
    {
        if (erath[i]==0)
            prime++;

    }

    fout<<prime;

}