#include "bits/stdc++.h"
#define REP(i,n,N) for(int i=(n); i<(N); i++)
#define RREP(i,n,N) for(int i=(N-1); i>=n; i--)
#define CK(n,a,b) (a)<=(n)&&(n)<(b)
#define ALL(v) (v).begin(),(v).end()
#define p(s) cout<<(s)<<endl
typedef long long ll;
using namespace std;
const int inf =1e9+7;


int main(){
    int n;
    while(cin>>n){
        int a[110];
        int sum[110];
        sum[0]=0;
        int ans=inf;
        REP(i,0,n){
            cin>>a[i];
            sum[i+1]=sum[i]+a[i];
        }
        for(int i=1;;i+=2){
            if(i/2*(i/2+1)+(i+1)/2>sum[n]) break;
            int now=1;
            int cnt=0;
            int tmp=0;
            if(i<n) cnt += (sum[n]-sum[i]);
            REP(j,0,min(i,n)){
                if(a[j]>now)cnt+=a[j]-now;
                if(j<i/2) now++;
                else if(j>=i/2) now--;
            }
            ans = min(ans,cnt);
        }
        p(ans);
    }
    return 0;
}