/*
    "TLE is like the wind, always by my side"
    - Yasuo - 2022 -
*/
#include <bits/stdc++.h>
#define debug(x) cerr << #x << " " << x << "\n"
#define debugs(x) cerr << #x << " " << x << " "

using namespace std;

bool c[2000001];

int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    int n,i,j,rez;
    fin >> n;
    for(i=2;i*i<=n;i++)
    {
        if (!c[i])
        {
            for (j=i*i;j<=n;j+=i)
            {
                 c[j]=1;
            }
        }
    }
    rez=0;
    for (i=2;i<=n;i++)
    {
        if (!c[i])
        rez++;
    }
    fout << rez;
}