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

k=max(0,T//A)
if T-k*A>=0:
    ANS=min(ANS,k*X+T-k*A)

#print(k,ANS)

k=max(0,(T+A-1)//A)
rest=k*A-T

l=(rest+B-1)//B

ANS=min(ANS,k*X+l*Y+T-k*A+l*B)

print(ANS)