/64位整数乘法
ULL res = 0;
while(b)
{
if(b & 1) res = (res + a) % c;
b >>= 1;
a = (a + a) % c;
}
/
/*快速幂

ll qsm(ll a,ll b, ll c)
{
ll res = 1;
while(b)
{
if(b&1) res = resa%c;
b/=2;
a=aa%c;
}
return res;
}

*/