import sys
#input = sys.stdin.readline
#input = sys.stdin.buffer.readline #文字列はダメ
#sys.setrecursionlimit(1000000)
#import math
#import bisect
#import itertools
#import random
#from heapq import heapify, heappop, heappush
from collections import defaultdict 
#from collections import deque
#import copy #DeepCopy: hoge = [_[:] for _ in hogehoge]
#from functools import lru_cache
#@lru_cache(maxsize=None)
MOD = pow(10,9) + 7
#MOD = 998244353
#dx = [1,0,-1,0]
#dy = [0,1,0,-1]
#dx8 = [1,1,0,-1,-1,-1,0,1]
#dy8 = [0,1,1,1,0,-1,-1,-1]

def main():
    T = int(input())
    X,A = map(int,input().split())
    Y,B = map(int,input().split())
    MAX = pow(10,7) + 5

    ans = 1 << 60
    # 戻る回数
    for i in range(MAX):
        nokori = T + B*i
        if nokori < 0:
            continue
        temp = Y*i
        j = nokori//A
        temp += j*X + (nokori - j*A)
        # print(i,temp)
        ans = min(ans, temp)
    print(ans)

if __name__ == '__main__':
    main()