Find the domain of the relation S given below:

S={(4,10),(12,9),(13,8),(11,4),(5,18)}\displaystyle {S}={\left\lbrace{\left(-{4},{10}\right)},{\left(-{12},-{9}\right)},{\left({13},-{8}\right)},{\left(-{11},-{4}\right)},{\left({5},{18}\right)}\right\rbrace}

D={}