import sys
input = sys.stdin.readline

T=int(input())
X,A=map(int,input().split())
Y,B=map(int,input().split())

ANS=1<<100

if T>=0:
    ANS=T

for i in range(3*10**7+5):
    rest=T+i*B

    if rest<0:
        continue

    k=rest//A

    ANS=min(ANS,i*Y+k*X+rest-k*A)

print(ANS)