[amibroker] How to Specify a Starting Date for a Plot of Portfolio Value

[ldriker]

How might I cause the following plot of portfolio value to commence 
processing on and after a specified date, for example, June 30, 
2006? Thank you.

_SECTION_BEGIN("Portfolio Value");
N = 5;
CSH = 0;
SYM = "ABT,A,AA,AMZN,AXP";
SHR="100,200,300,400,500";
XYZ = 0;
{ 
for( i = 0; i < N; i++ ) 
{ 
f = Foreign( StrExtract( SYM , i) , "C" ) * StrToNum(StrExtract( 
SHR , i )); 
if( i == 0 ) XYZ = f + CSH; 
else XYZ = XYZ + f;
}  }
SetChartOptions(0,chartShowDates);
Plot( XYZ, "Portfolio Value", colorGreen );
_SECTION_END();