principal,payment,months = map(int,input().split())
def move(rate):
    left = principal
    for _ in range(1,months+1):
        left = (1+rate)*left-payment
    return left
low,high = 0,1
while high-low>0.00001:
    mid = (low+high)/2
    result = move(mid)
    if result==0:
        break
    if result>0:
        high = mid
    else:
        low = mid
rate = mid*100
print('{:.1f}'.format(rate))