#!/bin/sh

Y=`yesterday`
M=`echo $Y | sed 's/....\(..\)../\1/'`

if [ $# -eq 0 ]
then
	A=0
else
	A=$1
fi

if [ $A -gt 0 ]
then
	if [ $A -gt $M ]
	then
		YEAR=-1
	else
		YEAR=0
	fi
	date --date "-1 day $A month $YEAR year `echo $Y | sed 's/....$/0101/'`" +%Y%m%d
else
	date --date "-1 day `expr 1 + $A` month `echo $Y | sed 's/..$/01/'`" +%Y%m%d
fi