write a go solution for Description:
Farmer John has an array a of length n. He also has a function f with the following recurrence:

- f(1)=sqrta_1;
- For all i>1, f(i)=sqrtf(i-1)+a_i.

Note that f(i) is not necessarily an integer.

He plans to do q updates to the array. Each update, he gives you two integers k and x and he wants you to set a_k=x. After each update, he wants to know lfloorf(n)rfloor, where lfloortrfloor denotes the value of t rounded down to the nearest integer.

Input Format:
The first line contains n and q (1<=n,q<=2*10^5), the length of a and the number of updates he will perform.

The second line contains n integers a_1,a_2,ldots,a_n (0<=a_i<=10^18).

The next q lines each contain two integers k and x (1<=k<=n, 0<=x<=10^18), the index of the update and the element he will replace a_k with.

Output Format:
For each update, output an integer, lfloorf(n)rfloor, on a new line.

Note:
In the first test case, the array after the first update is [4,14,0,7,6]. The values of f are:

- f(1)=2;
- f(2)=4;
- f(3)=2;
- f(4)=3;
- f(5)=3.

Since lfloorf(5)rfloor=3, we output 3.

The array after the second update is [3,14,0,7,6]. The values of f, rounded to 6 decimal places, are:

- f(1)approx1.732051;
- f(2)approx3.966365;
- f(3)approx1.991573;
- f(4)approx2.998595;
- f(5)approx2.999766.

Since lfloorf(5)rfloor=2, we output 2.. Output only the code with no comments, explanation, or additional text.