gawk '
   BEGIN {
     for (i=-3;i<=3;i++)
     {
        cmd="date --date=\"" i "days\" \"+%b%d\""
        cmd | getline
        close(cmd)
        dy[$0]++
     }
   }
   { for (s in dy) if ($0 ~ "^" s "[^0-9]") print }' les