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