In this Optimization we will Cure all the infected person before moving to next country.

We will have two cases 

1. when x < arr[i]

2. x >= arr[i]

Case 1: x < arr[i]

Here we will cure all the infected person thus we will not increment i until x >= arr[i]

Case 2: x >= arr[i]

Since we have vaccines greater than the infected person we can use the vaccines equal to arr[i].

Example

12 19 20

x = 4

x < arr[0]

arr[0] = 12 - 4 = 8

And x becomes

x = 8

Example

12 19 20

x = 4

arr[0]  = 16

x  = 8

x < arr[0]

hence at day 2

arr[0] = 16 - 8 = 8

x = 16

Example

12 19 20

x = 4

arr[0]  = 16

x  = 16

x = arr[0]

hence at day 3

all patients can be cured.