#include <iostream>
#include <math.h>
#include <fstream>
using namespace std;
ifstream fin ("ciur.in");
ofstream fout ("ciur.out");


int main() {
int a[2000000];
int nr = 0, n, i, j;

fin >> n;
if(n>=2 && n<=2000000){
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++;
fout << nr << endl;
}
return 0;
}