In a magic square, the sum of the numbers in each row, column, and diagonal is always the same. Consider a 3x3 magic square where the sum of each row, column, and diagonal is 15. If the center number is 5 and the numbers in the corners are in the ratio 1:2:3:4, find the number in the top left corner. Let's think step by step and output the final answer within \boxed{}.
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