n,m = map(int,input().split())
a = list(map(int,input().split()))
b = list(map(int,input().split()))
u = [0]*(n+1); d = [0]*(n+1)
for i,(x,y) in enumerate(zip(a,b),1):
    u[i] = (y-x)%m; d[i] = (x-y)%m
dpv = [m]+[0]*n; dpu = [0]*(n+1); dpd = [0]*(n+1); dpe = [m]+[0]*n
for i in range(n):
    dpv[i+1] = min(dpv[i]+max(u[i+1]-u[i],0),dpu[i]+u[i+1]+m-u[i])
    dpu[i+1] = min(dpu[i]+max(u[i+1]-u[i],0),dpd[i]+u[i+1],dpv[i])
    dpd[i+1] = min(dpd[i]+max(d[i+1]-d[i],0),dpu[i]+d[i+1],dpe[i])
    dpe[i+1] = min(dpe[i]+max(d[i+1]-d[i],0),dpd[i]+d[i+1]+m-d[i])
print(min(dpv[n],dpu[n],dpd[n],dpe[n]))