A,B,C,D,E = map(int, input().split())

k = B-C#来る人
a = k*A
m = 0
i_1 = D

for i in range(1,a+1):
    if i == 1:
        m += D
    
    elif i%10:
        m += i_1
        
    elif E <= i_1:
        m += max(i_1-E,0)
        i_1 = max(i_1-E,0)
    else:
        m += i_1
        pass
    
print(m)