in pascal i used
  lcm := a*b div gcd(a,b);

i got WA

i changed line to
  lcm := trunc(1.0*a*b / gcd(a,b));
and got AC
i think i had arithmetic overflow

Post your code please ....

I dont understand well in pascal but i want to know your algorithms ...

Using my code , i got Time Out .... below is my code :

#include<stdio.h>

int p[1000],tmp[1000];
int n;

int go(int t,int i){
  int j,v;

  v=p[i];
  for(j=1;j<t;j++)
    v=p[v-1];
  return v;
}


int checkout(int t){
  int i;

  for(i=0;i<n;i++){
    tmp[i]=go(t,i);
    if(tmp[i] != i+1)
      return checkout(t+1);
  }
  return t;
}

int main(){
  int i;
  scanf("%d",&n);
  for(i=0;i<n;i++)
    scanf("%d",&p[i]);
  printf("%d\n",checkout(1));
  return 0;
}

let consider following :
(a**b means a*a*a*...*a (b times))

p ** k1(1) = 1
p ** k2(2) = 2
...
p ** kN(n) = n

i.e. order of #i is ki.

the order of entire permutation is a number that is devided by k1,
k2, .., kN. The lowest such number is lcm(k1, k2, ... , kN);

but

lcm(a, b) * gcd(a, b) = a * b;
that is lcm(a, b) = a * b / gcd(a, b);

Yep , That is realy a GOOD

Yep , that is a good idea ...

OKey!