Doesn't work is awful vague. Are there errors in the log?: Post the code and log in a code box opened with the {i} to maintain formatting of error messages. No output? Post any log in a code box. Unexpected output? Provide input data in the form of a dataset, the actual results and the expected results. Data should be in the form of a data step. Instructions here: https://communities.sas.com/t5/SAS-Communities-Library/How-to-create-a-data-step-version-of-your-dat... will show how to turn an existing SAS data set into data step code that can be pasted into a forum code box using the {i} icon or attached as text to show exactly what you have and that we can test code against.
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You need another sysfunc.
27 %let yymm = 1709;
28 %let example = %sysfunc(intnx(month,%sysfunc(inputn(&yymm.,yymmn4.)),0,e),date9);
29 %put example is &example.;
example is 30SEP2017
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