import pypyjit
pypyjit.set_param("max_unroll_recursion=-1")
import sys
sys.setrecursionlimit(10**7)

from functools import cache
import bisect
N,S = list(map(int,input().split()))
X = list(map(int,input().split()))
W = list(map(int,input().split()))

@cache
def f(l,r,now_left,having):
    if(l == X[0] and r == X[-1]):return 0

    ret = 1<<60
    if(not now_left):
        if(r < X[-1]):
            right = bisect.bisect_right(X, r)
            dist = X[right] - r
            ret = min(ret, f(l,X[right],False,having - W[right]) + dist * having)
        
        if(l > X[0]):
            left = bisect.bisect_left(X, l) - 1
            dist = r - X[left]
            ret = min(ret, f(X[left],r,True,having - W[left]) + dist * having)
    else:
        if(r < X[-1]):
            right = bisect.bisect_right(X, r)
            dist = X[right] - l
            ret = min(ret, f(l,X[right],False,having - W[right]) + dist * having)
        
        if(l > X[0]):
            left = bisect.bisect_left(X, l) - 1
            dist = l - X[left]
            ret = min(ret, f(X[left],r,True,having - W[left]) + dist * having)
    
    return ret

print(f(S,S,True,sum(W)))