POJ 1284 Primitive Roots

Primitive Roots

Time Limit:1000MS     Memory Limit:10000KB     64bit IO Format:%I64d & %I64u

Submit Status Practice POJ 1284

Description

We say that integer x, 0 < x < p, is a primitive root modulo odd prime p if and only if the set { (xⁱ mod p) | 1 <= i <= p-1 } is equal to { 1, ..., p-1 }. For example, the consecutive powers of 3 modulo 7 are 3, 2, 6, 4, 5, 1, and thus 3 is a primitive root modulo 7.
Write a program which given any odd prime 3 <= p < 65536 outputs the number of primitive roots modulo p.

Input

Each line of the input contains an odd prime numbers p. Input is terminated by the end-of-file seperator.

Output

For each p, print a single number that gives the number of primitive roots in a single line.

Sample Input

23
31
79

Sample Output

10
8
24

#include<stdio.h>
int getans(int n){
    int ans = n;
    for(int i=2;i<=n;i++)
        if(n%i==0){
            ans = ans / i * (i-1) ;
            while(n%i==0)    n /= i;
        }
    if(n > 1)    ans = ans/n*(n-1) ;
    return ans ;
}
int main(){
    int p;
    while(scanf("%d",&p)!=EOF){
        printf("%d\n",getans(p-1));
    }
    return 0;
}