#include <iostream>
#include <fstream>
using namespace std;
ifstream fi("ciur.in");
ofstream fo("ciur.out");
int ciur[2000000];
int countt = 0;
int main()
{
    int n;
    fi>>n;
    for(int i = 2; i <= n; ++i)
    {
        if(ciur[i] == 0)
        {
            countt++;
            for(int j = i + i; j <= n; j += i)
            {
                ciur[j] = 1;
            }
        }
    }
    fo<<countt;
}