Mobile Obi

#Mobile
# By : Deukaus / Matheus Santos
# OBI 2015 nivel junior f1
# python
# https://olimpiada.ic.unicamp.br/pratique/pj/2015/f1/mobile/

A = int(input())
B = int(input())
C = int(input())
D = int(input())

if A == (B + C + D) and D == (B + C) and B == C:
    print("S")
else:
    print("N")