#include <bits/stdc++.h>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int N;
int prim[50000];
int contor;
void citire()
{
    fin>>N;
    prim[0] = 1;
    prim[1] = 1;
    for(int i=2; i * i <= N; i++)
    {
        if(prim[i] == 0)
        {
            for(int j= i * i; j<=N; j += i)
            {
                prim[j] = 1;
            }
        }
    }
    for(int i=2; i<=N; i++)
    {
        if(prim[i] == 0)
            contor++;
    }
    fout<<contor<<"\n";
}
int main()
{
    citire();
    return 0;
}