#include<iostream>
#include<numeric>
using namespace std;

int main(){
    int n;
    cin >> n;

    int a[101] = {};
    for(int i = 0; i < n; i++) cin >> a[i];

    int sum = accumulate(a, a+101, 0);
    int m = 1;
    while((m+1)*(m+1) <= sum)   m++;

    int residual = sum - m*m;
    int diff = 0;
    for(int i = 0; i < m; i++){
        diff += abs(a[i] - (i+1));
    }
    for(int i = m; i < m+m-1; i++){
        diff += abs(a[i] - (m+m-i-1));
    }
    for(int i = m+m-1; i < n; i++){
        diff += a[i];
    }

    int ans = residual + (diff-residual) / 2;
    cout << ans << endl;

    return 0;
}