n=int(input())
A=list(map(int,input().split()))
for i in range(2*n):
    A[i]=(A[i],i+1)

A.sort()
ans=0
for i in range(n):
    ans+=abs(A[i][0]-A[2*n-1-i][0])
print(ans)
for i in range(n):
    print(A[i][1],A[2*n-1-i][1])