#include<iostream>
#include<fstream>
using namespace std;
int v[1000001];
int main ()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    int i,n,j,s=1;
    f>>n;
    for(i=1;i<=n/2;i++)
    {
        if(v[2*i+1]==0)
            for(j=(2*i+1)*(2*i+1);j<=n*n;j+=2*i+1)
                v[(j-1)/2]=1;
    }
    for(i=1;i<=n/2&&i*2+1<n;i++)
            if(v[i]==0)
                s++;
    g<<s;
}