Ta có:
`{2023}/{2020}={2020+3}/{2020}={2020}/{2020}+3/{2020}`
`\qquad =1+3/{2020}`
`\qquad =1+1/{2020}+1/{2020}+1/{2020}`
`\qquad >1+1/{2021}+1/{2022}+1/{2023}`
$\\$
`M={2020}/{2021}+{2021}/{2022}+{2022}/{2023}+{2023}/{2020}`
`M>{2020}/{2021}+{2021}/{2022}+{2022}/{2023}`
`\qquad +1+1/{2021}+1/{2022}+1/{2023}`
`M>({2020}/{2021}+1/{2021})+({2021}/{2022}+1/{2022})`
`\qquad +({2022}/{2023}+1/{2023})+1`
`M>1+1+1+1`
`M>4`
Vậy `M={2020}/{2021}+{2021}/{2022}+{2022}/{2023}+{2023}/{2020}>4`