#include <iostream>
#include <fstream>
using namespace std;

bool c[2000001];

int main()
{
    ifstream in("ciur.in");
    ofstream out("ciur.out");
    int n,i,j,q=0;
    in>>n;
    for(i=2;i*i<=n;i++)
        if(!c[i])
            for(j=i*i;j<=n;j+=i)
                c[j]=true;
    for(i=2;i<n;i++)
        if(!c[i])
            q++;
    out<<q;
    in.close();
    out.close();
    return 0;
}