#include<bits/stdc++.h>
#define rep(i,a,b) for(int i=int(a);i<int(b);++i)
using namespace std;
typedef long long ll;
int INF = (1LL << 30) - 1;
int MOD = 1e9+7;
main(){
    int N;
    cin >> N;
    vector<int> V(210 + N);
    rep(i,0,N)cin >> V[i];
    int sum = 0,mini = INF;
    rep(i,0,N)sum += V[i];

    //i := 最大値がiとなるピラミッド列
    for(int i = 1;i * i <= sum;i++){
        int dif = 0,use = 0;
        rep(k,0,i * 2 - 1){
            int num = i - abs(i - k - 1);
            dif += max(V[k] - num , 0);
            use += V[k];
        }
        dif += sum - use;
        mini = min(mini, dif);
        //cout << "i:" << i << " " << mini << endl;

    }
    cout << mini << endl;
}