Calculating the degree of the lowest non-zero term of a polynomial

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I was wondering if there was a way to calculate the degree of the lowest non-zero term of a polynomial. What I mean by this is that, for example, for x^2+7x^4+x^5, I would like to return 2, for 7x+x^2+7x^4+x^5 I would like to return 1, for 1+7x+x^2+7x^4+x^5 I would like to return 0, ect...