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

ans = 10**10

for i in range(T//A+1000):
    for j in range(T//B+1000):
        tmp1 = i*A
        tmp2 = j*(B*-1)
        tmp3 = max(0,T-tmp1-tmp2)
        if tmp1+tmp2+tmp3 == T:
            ans = min(ans,i*X+j*Y+tmp3)
            #print(i,j,tmp3,"sum",i+j+tmp3)

print(ans)