Solution I by Hongwei Chen

Amdeberhan, T; Moll, VH; Bataille, M; Chapman, R; Dutta, R; Fitzsimmons, PJ; Fritze, D; Grivaux, N; Herman, EA; Kieffer, JC; Kouba, O; Kuczma, ME; Lindsey, JH; Omarjee, M; Omey, E; Singer, NC; Smith, JC; Stenger, A; Stong, R; Tauraso, R

AMERICAN MATHEMATICAL MONTHLY, 2017; 124 (1): 84