#include<iostream>
#include <fstream>
#include <bitset>
using namespace std;
#define MAXN 2000000
int n;
bitset<MAXN+1> b;
int main() {
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    fin>>n;
    int i,j;
    for (i=3; i*i<=n; i+=2)
        if (!b[i]) {
            for (j=i*i; j<=n; j+=2*i)
                b[j]=1;
        }
    fout<<(n+1)/2-b.count();
}