How to place money into 4 symbol?

I have 4 symbols and they have different starting date:
starting date
1.2015/2/9
2.2016/3/9
3.2017/8/9
4.2017/8/5
I want to allocate 1/4 money into every symbol. But my afl only buy 1 and 2 symbol.
How to modify the amibroker to buy 4 symbols.

Thank you very much.

SetOption("InitialEquity", 100000); 
SetOption("CommissionMode", 3); //count hand cost by how much future
SetOption("CommissionAmount", 0.01); //one future hand cost 50 dollars
SetOption("MaxOpenPositions",4);
SetBacktestMode(backtestRegularRaw);

NumberHeld=4;//Optimize("NumberHeld",1,1,10,2);

//Allocate funds equally among all issues
PositionSize = -100/(NumberHeld);

Buy = 1;
Sell= 0;