#include <iostream>
#include <fstream>
#include <bitset>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int ciurprime[2000000];
void Ciur(int N)
{
    ciurprime[0] = ciurprime[1] = 1;
    for (int i = 4; i < N; i += 2)
        ciurprime[i] = 1;
    for (int i = 3; i * i < N; i += 2) {
        if (ciurprime[i] == 0)
            for (int j = i * i; j < N; j += 2 * i)
                ciurprime[j] = 1;
    }

}
int main()
{
    int n,cnt = 0;
    fin>>n;
    Ciur(n);
    for(int i=1;i<=n;i++)
        if(ciurprime[i]==0) cnt++;
    fout<<cnt-1;


}