判定一个数是否是质数

import java.util.Scanner;

public class First {
 public static void main(String[] args) {
  boolean result;
  Scanner in = new Scanner(System.in);
  int a = in.nextInt();
  result = isprime(a);
  if (result==false) {
   System.out.println("shi");
  } else
   System.out.println("fou");
 }
 public static boolean isprime(int a) {
  boolean flag =false;
  long b = Math.round(Math.sqrt(a));
  if (b == 2) {
   return true;
  }
  for (int c = 3; c <= b; c++) {
   if (a % c == 0) {
    return false;
   }
  }
  return flag;
 }
}