suppose n == 2 ;

then you will have [1, 2] ;

the first situation

if you guess is 2 , you will have two options given. first , you are correct , second you are wrong .

if you are correct , then pay 0 $, but if you are wrong, then you pay 2$

the worst case for the above is 2$ ;

the second situation

if you guess is 1 , you will still have two options given. first , you are correct , second you are wrong .

if you are correct , then pay 0 $, but if you are wrong, then you pay 1$

the worst case for the second situation is 1$ ;

According to above, the money you have to have is the MIN (worst case for first situation , worst case for second situation) which is 1 $.

make sense ?

-Scott