#!/usr/bin/sh

check_done() {
        if [ $month -eq 1 -o $month -eq 3 -o $month -eq 5 -o $month -eq 7 -o $month -eq 8 -o $month -eq 10 -o $month -eq 12 ]
        then
                daysofmth=31
        elif [ $month -eq 2 ]
        then
                if [ `expr $year % 100` -eq 0 -a `expr $year % 400` -eq 0 ]
                then
                        daysofmth=29
                elif [ `expr $year % 100` -ne 0 -a `expr $year % 4` -eq 0 ]
                then
                        daysofmth=29
                else
                        daysofmth=28
                fi
        elif [ $month -eq 4 -o $month -eq 6 -o $month -eq 9 -o $month -eq 11 ]
        then
                daysofmth=30
        fi
        julday=`expr $julday - $daysofmth`
        if [ $julday -lt 0 ]
        then
                done=1
                julday=`expr $daysofmth + $julday`
        elif [ $julday -eq 0 ]
        then
                done=1
                julday=$daysofmth
        fi
}
#########  main script starts here
if [ $# -ne 1 ]
then
        echo "Usage: tonfro <delta>"
        exit 1
fi
julday=`expr \`date +%j\` + $1`
year=`date +%Y`
month=0
while [ $julday -le 0 ]
do
        year=`expr $year - 1`
        if [ `expr $year % 100` -eq 0 -a `expr $year % 400` -eq 0 ]
        then
                julday=`expr $julday + 366`
        elif [ `expr $year % 100` -ne 0 -a `expr $year % 4` -eq 0 ]
        then
                julday=`expr $julday + 366`
        else
                julday=`expr $julday + 365`
        fi
done

done=0

while [ $done -ne 1 ]
do
        month=`expr $month + 1`
        if [ $month -eq 13 ]
        then
                year=`expr $year + 1`
                month=1
        fi
        check_done
done

printf "%d-%.2d-%.2d\n" $year $month $julday