#include <iostream>
#include <fstream>

using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");

int main()
{
    int n,i,p,cont=0;
    in>>n;
    bool prim[n+1];
    for(p=2;p<=n;p++) prim[p]=1;
    for(p=2;p<=n;p++)
    {
        if(prim[p])
        {
            cont++;
            for(i=1;i<=n/p;i++) prim[p*i]=0;
        }
    }
    out<<cont;
    return 0;
}
/*#include <fstream>
#include <math.h>

using namespace std;
ifstream in;
ofstream out;
    bool a[2000002];
int main()
{
    in.open("ciur.in");
    out.open("ciur.out");
    int nr=0,n,i,j;

    in>>n;
    for (i=2; i<=n; i++)
        a[i]=1;
    for (i=2; i<=sqrt(n); i++)
        if (a[i])
            for (j=i; j<=n/i; j++)
                a[i*j]=0;
    for (i=2; i<=n; i++)
        if (a[i]) nr++;
    out<<nr;
    out.close();
    return 0;
}*/