Sum formulae

I have data across five (5) sheets. I will make this as east to explain as I can. I am a beginner. I have numerical values in A1 for five sheets. (Sheet 1, A1; Sheet 2, A1, et cetera). For the sixth sheet, I want it to display a total for all the values in A1 across the sheets. This is where it becomes tricky: Data is entered daiy, so the total will change; albeit, I don't want anything to display in the cell until a numbered is entered; id est, I don't want the cell to contain anything until numbers are entered. Example: If sheets one and two have a 1 in them, Sheet six would display a two. The next day, if I were to add a 1 in Sheet 3, A1, sheet six would display a three. I have several function I'll need to do, but I need to grasp the basics. This is as basic as I can make it. I have searched IF, AND, OR, & SUMIF functions. I'm missing something. ANY help shall be greatly appreciated.
Let me know if I need to elucidate my post. Thanks!