View Compilation Error

0_0_26053614_2544.cpp: In function 'll sum(ll)':
0_0_26053614_2544.cpp:30:30: error: invalid operands of types '__gnu_cxx::__promote_2<int, int, double, double>::__type {aka double}' and 'const int' to binary 'operator%'
  ret = (ret * pow(3,mod-2)) %mod;
                              ^