(M+(n-1)m)*v1-mv=0
L1=L+L*v1/v
(M+(n-2)m)v2-mv=(M+nm)*v1
L2=L1+L1*v2/v1
.
.
.
M*vn-mv=(M+m)*vn-1(这里的n,n-1是下标)
Ln=Ln-1*(1+vn/vn-1)(这里的n,n-1是下标)
S=Ln-L
(M+(n-1)m)*v1-mv=0
L1=L+L*v1/v
(M+(n-2)m)v2-mv=(M+nm)*v1
L2=L1+L1*v2/v1
.
.
.
M*vn-mv=(M+m)*vn-1(这里的n,n-1是下标)
Ln=Ln-1*(1+vn/vn-1)(这里的n,n-1是下标)
S=Ln-L