快速幂

#define LL long long
#define Mod 1000;//题面给Mod；
LL pow(LL a,LL b)
{
 LL res = 1;
 LL base = a;
 while (b)
 {
  if (b & 1) res = res * base%Mod;
   base = base * base%Mod;
   b >>= 1;
 }
 return res;
}