phrase = "C'est ainsi que le cygne fit signe"
lettres = ""

for i in range(len(phrase)):
    presence = False
    for j in (range(len(lettres))):
        if phrase[i] == lettres[j]:
            presence = True
    if presence == False:
        if i != 0:
            lettres += " ; "+phrase[i]
        else:
            lettres += phrase[i]
            
print(lettres)