1978 IMO Problems/Problem 1

Problem

$m$ and $n$ are positive integers with $m < n$. The last three decimal digits of $1978^m$ are the same as the last three decimal digits of $1978^n$. Find $m$ and $n$ such that $m + n$ has the least possible value.

Solution

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Solution is available here: https://www.youtube.com/watch?v=SRl4Wnd60os

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