S = input()
a1 = 0
for i in range(len(S)):
    a1 += int(S[i])
a1 = str(a1)
for i in range(99):
    a2 = 0
    for j in range(len(a1)):
        a2 += int(a1[j])
    a1 = a2
    a1 = str(a1)
print(a1)