//Codeforces Round #174 (Div. 2) A Cows and Primitive Roots
import java.io.*;
import java.math.*;
import java.text.*;
import java.util.*;
//Codeforces
public class MainCodeforces1 {
private static MyScanner in;
private static PrintStream out;
public static void main(String[] args) throws IOException {
// helpers for input/output
boolean LOCAL_TEST = false;// change to false before submitting
out = System.out;
if (LOCAL_TEST) {
in = new MyScanner("E:\\zin2.txt");
}
else {
boolean usingFileForIO = false;
if (usingFileForIO) {
// using input.txt and output.txt as I/O
in = new MyScanner("input.txt");
out = new PrintStream("output.txt");
}
else {
in = new MyScanner();
out = System.out;
}
}
solve();
}
private static void solve() throws IOException
{
int p = in.nextInt();
int nx = 0;
for (int x = 2; x < p; x++) {
int xx = x;
boolean primroot = true;
for (int j = 1; j < p - 1; j++) {
if ((xx - 1) % p == 0) {
primroot = false;
break;
}
xx = xx * x % p;
}
if (primroot) {
if ((xx - 1) % p != 0) {
primroot = false;
}
}
if (primroot)
nx++;
}
if (p == 2)
nx = 1;
out.println(nx);
}
// =====================================
static class MyScanner {
Scanner inp = null;
public MyScanner() throws IOException
{
inp = new Scanner(System.in);
}
public MyScanner(String inputFile) throws IOException {
inp = new Scanner(new FileInputStream(inputFile));
}
public int nextInt() throws IOException {
return inp.nextInt();
}
public long nextLong() throws IOException {
return inp.nextLong();
}
public double nextDouble() throws IOException {
return inp.nextDouble();
}
public String nextString() throws IOException {
return inp.next();
}
}
}
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