Help me with my code for WITMATH

I submitted my code in python of WITMATH during the contest and got AC.
When i was submitting the same using C++ it was giving TLE though i had taken all steps to prevent overflow. Please can anyone help. Here’s my code:

/*aayushagarwal*/
#include<cstdio>
#include<cstdlib>
using namespace std;
unsigned long long int mult(unsigned long long int a,unsigned long long int b,unsigned long long int c)
{
      unsigned long long int x=0,y=a%c;
      while(b>0)
      {
            if(b%2==1)
            {x=x+y;
                  if(x>c)x=x%c;
            }
            y=y+y;
            if(y>c)y=y%c;
            b/=2;
      }
      return x%c;
}
unsigned long long int modulo( unsigned long long int a, unsigned long long  int b, unsigned long long  int c)
{
      unsigned  long long int x = 1;
      unsigned long long int y = a;
      while (b>0)
      {
            if (b%2==1)
                  x = mult(x,y,c);
            y = mult(y,y,c);
            b = b/2;

      }
      return x%c;
}


bool millerRabin(unsigned long long int N,unsigned long long int iteration)
{
      if (N<2)
            return false;
      if (N!=2&&N%2==0)
            return false;

      unsigned  long long int d=N-1;
      while (d%2==0)
            d = d/2;

      for (long long int i=0;i<iteration;i++)
      {

            unsigned long long int  a = rand()%(N-1)+1;
            unsigned long long int temp = d;
            unsigned long long int x = modulo(a,temp,N);
            while (temp!=N-1 && x!=1 and x!=N-1){
                  x = mult(x,x,N);
                  temp = temp*2;
            }

            if (x!=N-1 && temp%2==0)
                  return false;

      }
      return true;
}
int main()
{   
      unsigned long long int n;int t;

      scanf("%d",&t);
      while(t--)
      {
            bool prime=false;
            scanf("%llu",&n);
            if(n==2||n==3)
                  printf("%llu

",n);
else if(n==4)
printf("3
");
else if(n==5||n==6)
printf("5
");
else if(n==7||n==8||n==9||n==10)
printf("7
");
else if(n==11||n==12)
printf("11
");

            else
            {
                  while(!prime)
                  {       
                        if(n%2!=0 && n%3!=0 && n%5!=0 && n%7!=0 && n%11!=0)
                              prime=millerRabin(n,20);
                        n--;
                  }
                  printf("%llu

",n+1);
}
}

      return 0;
}

Kindly post your question on the editorial page of the respective problem here: http://discuss.codechef.com/questions/9723/witmath-editorial. You will get your answer to your query.