I compiled & run code first in my mind & then on my machine.I got "abcdef"

.When i was doing from my mind,i thought that Set always contains
unique elements, and therefore no use of line 3 & line 4.Since s1 & s are already added at Line 1 7 Line 2 respectively(remebering that v r adding is Set...unique)
Bye.
Viki.
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Count the flowers of ur garden,NOT the leafs which falls away!