#include <iostream>
#include <fstream>
using namespace std;
int n,k=0,c[2000001];
void ciur()
{int i,j;
    for (i=4;i<=n;i+=2)
      c[i]=1;
    for (i=3;i*i<=n;i+=2)
        if (c[i]==0)
            for (j=i*i;j<=n;j+=i)
            c[j]=1;
    for (i=2;i<=n;i++)
        if (c[i]==0)
        k++;
}
int main()
{
    ifstream in("ciur.in");
    ofstream out("ciur.out");
    in>>n;
    ciur();
    out<<k;
}