ex1 s10

def verif(ch):
    test=True
    i=0
    while test==True and i!=len(ch):
        if not(ch[i].upper() in ["A","B","C","D","E","F"] or "0"<=ch[i].upper()<="9"):
            test=False
        i=i+1
    return test==True
def saisie():
    while True:
        ch=input("ch:")
        if len(ch)>0 and verif(ch): break
    return ch
def convertir(ch):
    s=0
    if ch=="A":
        s=10
    elif ch=="B":
        s=11
    elif ch=="C":
        s=12
    elif ch=="D":
        s=13
    elif ch=="E":
        s=14
    elif ch=="F":
        s=15
    else:
        s=int(ch)
    return s
def calcul(ch):
    p=0
    x=0
    bi=16**(len(ch)-1)
    for i in range(len(ch)):
        x=bi*convertir(ch[i])
        p=x+p
        bi=bi//16
    return p
ch=saisie()
print("n=",calcul(ch))