Codeforce---educational codeforces Round 3 Load balancing The Chase

It's my idea to see this question, but it's definitely about the average, but then I don't know what to do.

After reading the great God's coefficient, the original discovery is so simple, but I do not know why must be mean and average plus 1, rather than mean and average minus 1;

Okay, here's the code for the Great God:

#include <iostream> #include <cstdio> #include <algorithm>using namespace Std;int a[100005];int Main ( ) {    int n;scanf ("%d", &n);    for (int i=1;i<=n;i++)        scanf ("%d", &a[i]);    Sort (a+1,a+1+n);    A long long sum = 0;    for (int i=1;i<=n;i++)        sum+=a[i];    int p = sum/n;    int n1 = n-sum%n;    int ans = 0;    for (int i=1;i<=n1;i++)    {        if (p<=a[i]) break;        Ans+=p-a[i];    }    for (int i=n1+1;i<=n;i++)    {        if (a[i]>p) break;        Ans+=p+1-a[i];    }    printf ("%d\n", ans);}

Codeforce---educational codeforces Round 3 Load balancing The Chase