#include <iostream>
#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bool prim[2000010];
int nr[2000001], N;
int main()
{
    prim[0] = prim[1] = 1;
    for(int i = 2;i * i <= 2000000;i++){
    if(prim[i] == 0){
            nr[i] += nr[i - 1] + 1;
        for(int j = 2;j * i <= 2000000;j++)
            prim[j * i] = 1;
        }
    else nr[i] += nr[i - 1];
    }
    in >> N;
    out << nr[N];
    return 0;
}