import sys
input = sys.stdin.readline
from collections import *

T = int(input())
X, A = map(int, input().split())
X = min(X, A)
Y, B = map(int, input().split())
ans = 10**18

for i in range(10**8):
    if T+i*B>=0:
        s, a = divmod(T+i*B, A)
        cost = a+s*X+i*Y
        ans = min(ans, cost)

print(ans)