fix cursor starting in wrong spot

main.js

@@ -175,7 +175,7 @@ function keyPress(c) {
 	const begin = currentInput.value.slice(0, selectionStart);
 	const end = currentInput.value.slice(selectionEnd);
 	currentInput.value = begin + c + end;
-	currentInput.setSelectionRange(selectionEnd+1, selectionEnd+1);
+	currentInput.setSelectionRange(selectionStart+1, selectionStart+1);
 }
 
 document.querySelector("#expr").addEventListener("focus", setCurrentInput);