List<Integer>ls=new List<Integer>();
Integer i=0;
for(integer i=1;i<=20;i++){
ls.add(i);
}
system.debug(ls);
while(i<20){
if(Math.mod(i,2)==0){
ls.add(i);
}
else{
system.debug('out of limit');
}
system.debug(ls);
}
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