#variablen
characters=['t','a','c','o']
#Befehle
output = ''
length=len(characters)
i=0
while(i < length):
    output = output + characters[i]
    i=i+1


length=length*-1
i=-2

while (i >= length):
    output= output + characters[i]
    i=i-1

print(output)