#include <cmath>
#include <fstream>
using namespace std;
bool a[2000000];
int main()
{
    int nr=0,n,i,j;
    ifstream in("ciur.in");
    ofstream out("ciur.out");
    in>>n;
    a[2]=1;
    for(i=3;i<=n;i=i+2)
    a[i]=1;
    for(i=3;i<=sqrt(n);i=i+2)
    for(j=1;j<=n/i;j++)
    a[i*j]=0;
    if(n>2)
    nr++;
    for(i=3;i<=n;i=i+2)
    if(a[i])
    nr++;
    out<<nr;
    return 0;
    }