#include <fstream>

using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bool a[2000001];
int main()
{
    int n,i,j,s=0;
    in>>n;
    for(i=4;i<=n;i+=2)
    {
        a[i]=1;
    }
    for(i=3;i<=n;i+=2)
    {
        for(j=2;i*j<=n;j++)
            a[i*j]=1;
    }
    a[0]=1;a[1]=1;
    for(i=2;i<=n;i++)
        if(a[i]==0)
        s++;
    out<<s;
}