#include <iostream>
#include <fstream>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

long long n, ciur[2000001], i, j, nrprime = 1;
int main()
{
    fin >> n;
    ciur[0] = 1;
    ciur[1] = 1;
    for(i = 4; i <= n; i += 2) {
        ciur[i] = 1;
    }
    for(i = 3; i <= n; i +=2) {
        if(ciur[i] == 0) {
            nrprime++;
            for(j = i*i; j <= n; j += i) {
                ciur[j] = 1;
            }
        }
    }
    fout << nrprime;
    return 0;
}