#include <iostream>
#include <fstream>

using namespace std;
long long v[2000001],x,s,a,i,j,n;
int main()
{
   ifstream in("ciur.in");
   ofstream out("ciur.out");
   v[0]=v[1]=1;
    for(i=2;i*i<=2000000;i++)
    {
        for(j=i*2;j<=2000000;j+=i)
        v[j]=1;

    }
    in>>n;
for(i=2;i<n;i++)
if(v[i]!=0)
s++;
out<<s;




    return 0;
}