#include <iostream>
#define nmax 2000000
#include <fstream>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

bool c[nmax];

int i,j,n;

int main()
{
    c[0]=c[1]=1;
    for(i=2;i*i<nmax;i++)
    {
        if(c[i] == 0)
        {
            for(j=i+i;j*j<nmax;j+=i)
                c[j]=1;
                c[j]=1;
        }
    }
    fin>>n;
    int nr=0;
    for(i=n;i>=2;i--)
        if(c[i] == 0)
            nr++;
    fout<<nr;
    return 0;
}