def main():
    A, B, C, D, E = map(int, input().split())
    candys = A * (B - C)
    X = D
    total = 0
    for i in range (1, candys + 1):
        if i != 1 and i % 10 == 0 and X - E >= 0:
            X -= E
        total += X
    print(total)

if __name__ == '__main__':
    main()