View Compilation Error

0_0_20617926_22714.cpp: In function 'll sum(ll, ll)':
0_0_20617926_22714.cpp:9:21: error: invalid operands of types '__gnu_cxx::__promote_2<long long int, long long int, double, double>::__type {aka double}' and 'const ll {aka const long long int}' to binary 'operator%'
  return pow(n, k) % mod;
                     ^