#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
bool v[2000003];
int nrp=0,n,i,j;
int main()
{
    f>>n;
    nrp=n-1;
    v[0]=1;v[1]=1;
    for(i=2;i<=sqrt(n)+1;i++)
        if(v[i]==0)
            for(j=i*2;j<=n;j+=i)
            {
                if(v[j]==0)
                    nrp--;
                v[j]=1;
            }
    g<<nrp;
}