#include <bits/stdc++.h>
#include <math.h>
#include <fstream>
using namespace std;

typedef long long int lint;

ifstream fin("ciur.in");
ofstream fout("ciur.out");
int main()
{
    lint n, cnt = 0, maxim = 0;
    fin>>n;
    bool v[2000001];
    bool done = false;
    for (lint i = 2; i <= sqrt(2000001); i ++)
    {
        for(lint j = 2; j <= 2000001 / i; j++ )
        {
            v[j*i] = 1;
        }
    }
    for(lint i = 1; i <= 2000001 && done == 0; i++)
    {
        if(v[i] == 0)
        {
            if(i != 1)
            {
                if(i >= maxim && i <= n)
                    cnt++;

                if(i >= n)
                {
                    fout<<cnt;
                    done = 1;
                }
            }
        }
    }

    fin.close();
    fout.close();
    return 0;
}