In problem D, for test case 2, 1, 5, 6, 4, 3 why spell of 7 is not the minimum because if we start with index 4(value = 6) and damage = 7, then index = 3 getting damage 6, then index 5 getting damage 5, index 6 getting damage 4 and index 2 and 1 getting damage 3 and 2 respectively. Can anyone suggest where I am doing wrong?

currently in div3 contest,i got a rating of 4953 despite submitting first 3 questions in 1:15 mins and some other guy submitting the same 3 questions in 1:30 mins got better ranking than me like around 4200. Can someone explain me for the sake of understanding that how it works?