Let $x$ and $y$ be real numbers such that $-1 < x < y < 1.$  Let $G$ be the sum of the infinite geometric series whose first term is $x$ and whose common ratio is $y,$ and let $G'$ be the sum of the infinite geometric series whose first term is $y$ and whose common ratio is $x.$  If $G = G',$ find $x + y.$
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You are a helpful assistant.<|im_end|>
<|im_start|>user
Let $x$ and $y$ be real numbers such that $-1 < x < y < 1.$  Let $G$ be the sum of the infinite geometric series whose first term is $x$ and whose common ratio is $y,$ and let $G'$ be the sum of the infinite geometric series whose first term is $y$ and whose common ratio is $x.$  If $G = G',$ find $x + y.$
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
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Let $x$ and $y$ be real numbers such that $-1 < x < y < 1.$  Let $G$ be the sum of the infinite geometric series whose first term is $x$ and whose common ratio is $y,$ and let $G'$ be the sum of the infinite geometric series whose first term is $y$ and whose common ratio is $x.$  If $G = G',$ find $x + y.$
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