The normal thing to do is write the date at the end of a month. However, sometimes people use other abbreviations for "at the end of" or they misspell it. This article breaks down what different abbreviations mean and what they stand for.
It is usually written as a lower-case letter with three dots on top of it, which means that the month after that is in that year. For example, if you want to write April in 2018, you would type "4/2018".
The abbreviation for "at" can also be written as a period with an uppercase A on top of it and a slash through it.
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