#include <iostream>
#include <fstream>
using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

int N,cnt;
bool ciur[2000001];

int main()
{
    f >> N;
    cnt = 1; // 2 prim
    for ( int i = 3; i <= N ; i+=2 )
    {
        if ( ciur[i] == false )
        {
            cnt++;
            for ( int j = i+i; j <=N; j+=i )
            {
                ciur[j] = true;
            }
        }
    }
    g << cnt ;
    return 0;
}