---| stack |-----------------------------------------
pushed[0] = 5
pushed[1] = mon
pushed[2] = tue
pushed[3] = wed
pushed[4] = thu
pushed[5] = fri
after popping [fri] a[0]=4
after popping [thu] a[0]=3
after popping [wed] a[0]=2
after popping [tue] a[0]=1
after popping [mon] a[0]=0