def main():
    n,m,p,q = map(int,input().split())
    twice = [x %13 for x in range(p,p+q)]
    cur = 1 #現在の月
    cnt = 0#経過した月
    while n>0:
        if cur in twice:
            n -=2*m
        else:
            n -=m
        cur+=1
        cur%=13
        if cur ==0:cur=1
        cnt+=1
    print(cnt)
main()