#include <iostream>
#include <fstream>
#include <cmath>
#include <cstring>
using namespace std;
bool fr[2000002];
int nr=1,n,i,j;
int main()
{
ifstream fin("ciur.in");
ofstream fout("ciur.out");
fin>>n;
fr[1]=1;
for(i=4;i<=n;i=i+2)
    fr[i]=1;
for(i=3;i<=n;i=i+2)
    if(fr[i]==0)
{
    nr++;
    for(j=2*i;j<=n;j=j+i)
        fr[j]=1;
}
fout<<nr;
}