foo.cc: In function 'void solve()':
foo.cc:89:50: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   89 |                                 for(int i = 1; i < v.size() - 1; ++i)
      |                                                ~~^~~~~~~~~~~~~~

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