def parse(inFile):
    inFile.getInt()
    return inFile.getInts()

from operator import xor

def solve(values):
    if reduce(xor, values) != 0:
        return "NO"
    return sum(values)-min(values)

if __name__ == "__main__":
    from GCJ import GCJ
    GCJ(parse, solve, "/Users/lpebody/gcj/2011_q/", "c").run()