Given an array of N positive integers in random order (duplicates are possible), find a maximum sum that can be generated with more than one pair of array elements. If such sum doesn\'t exist, return -1.\n\nFunction signature (example in C++) is:\n```\nint FindMaxSum(std::vector<int>& numbers);\n```\n\nExamples:\n```\n{ 25, 4, 28, 1, 5, 1, 17, 2 }\n```\nMax sum is 30, from pairs (25, 5) and (28, 2).\n\n```\n{ 25, 15, 28, 1, 6, 17, 2 }\n```\nSum doesn\'t exist, result is -1.\n\nElements in an array aren\'t greater than 1,000,001.

Given an array of N positive integers in random order (duplicates are possible), find a maximum sum that can be generated with more than one pair of array eleme