#include <iostream>
#include <fstream>
#define NMAX 2000005
#define LL long long
#include <vector>
#include<bitset>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bitset <NMAX> isprime;
vector <int> pr;
int c;
void ciur()
{
    for(LL i=2;i<=NMAX;i++){
        if (isprime[i]==0){
            for (LL j=i*i;j<=NMAX;j+=i){
                isprime[j]=1;
            }
            pr.push_back(i);
        }
    }
}
int main()
{   int n;
    fin>>n;
    ciur();
    for(LL i=0;pr[i]<=n;i++){
        c++;
    }
    fout<<c;
    return 0;
}