Compilare: main.cpp: In function 'long long int solve(int)': main.cpp:38:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 38 | for (int i = 0; i < a.size(); i++) | ~~^~~~~~~~~~ main.cpp:43:15: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 43 | if (i == a.size() - 1) | ~~^~~~~~~~~~~~~~~