S=input()
ans = float('inf')
for i in range(len(S)):
	for j in range(i,len(S)+1):
		k = S[i:j]
		if k.count('c') >= 1 and k.count('w') >= 2:
			ans = min(ans, k)
if ans > len(S):
	ans = -1
print(ans)