#include <iostream>
#define LL long long
#define NMAX 2000005
#include <vector>
#include <bitset>
#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");

bitset < NMAX > esteprim;
vector <int>pr;
int n,v[NMAX],a,num;
void ciur() {
    for (LL i=2;i<=NMAX;i++) {
        if (esteprim[i]==0) {
            for (LL j=i*i;j<=NMAX;j+=i)
                  esteprim[j]=1;
            pr. push_back(i);
        }

    }


}


int main()
{
    f >> n;
    ciur();
    while (pr[a]<n) {
        num++;
        a++;
    }
    g << num;
    f.close();
    g.close();
    return 0;
}