#!/bin/sh
 X=50
 while ((X <= 1000))
 do
    mkdir DBL-0$X
    cp README  DBL-0$X/README
      ((X = X+50))
 done
 

X=1000
while ((X <= 2500))
do
    mkdir DBL-$X
    cp README  DBL-$X/README
     ((X = X+50))
done