#include <iostream>
#include <math.h>
#include<fstream>
using namespace std;

int main() {
ifstream f("ciur.in");
ofstream g("ciur.out");
int nr = 0, n, i, j;
f>> n;
int a[n];
for (i = 2; i <= n; i++)
a[i] = 1;
for (i = 2; i <= sqrt(n); i++)
if (a[i] != 0)
for (j = 2; j <= n / i; j++)
a[i*j] = 0;
for (i = 2; i <= n; i++)
if (a[i] != 0)
nr++;//Daca a[i]!=0, in cazul nostru cand a[i]==1, crestem contorul, de exemplu cand dam de numarul 2, nr ajunge 1, la numarul 3, nr ajunge 2, etc.
g<<nr;
return 0;
}