A, B, C, D, E = map(int, input().split())
cnt = (B-C)*A
ans = 0
X = 0
for i in range(cnt):
    if i==0:
        ans+=D
        X=D
    else:
        if (i+1)%10==0:
            if E<=X:
                ans+=X-E
                X = X-E
            else:
                ans+=X
        else:
            ans+=X
print(ans)