#include <bits/stdc++.h>
const long long INF = 1LL << 60;
const long long MOD = 1000000007;
const double PI = acos(-1.0);
#define rep(i, n) for (ll i = 0; i < (n); ++i)
#define rep1(i, n) for (ll i = 1; i <= (n); ++i)
#define rrep(i, n) for (ll i = (n - 1); i >= 0; --i)
#define perm(c) sort(ALL(c));for(bool c##p=1;c##p;c##p=next_permutation(ALL(c)))
#define ALL(obj) (obj).begin(), (obj).end()
#define RALL(obj) (obj).rbegin(), (obj).rend()
#define pb push_back
#define to_s to_string
#define len(v) (ll)v.size()
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end())
#define print(x) cout << (x) << '\n'
#define drop(x) cout << (x) << '\n', exit(0)
#define debug(x) cout << #x << ": " << (x) << '\n'
using namespace std;
using ll = long long;
typedef pair<ll, ll> P;
typedef vector<ll> vec;
typedef vector<vector<ll>> vec2;
typedef vector<vector<vector<ll>>> vec3;
template<class S, class T> inline bool chmax(S &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class S, class T> inline bool chmin(S &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
inline ll msb(ll v) { return 1 << (31 - __builtin_clzll(v)); }
inline ll devc(ll x, ll y) { return (x + y - 1) / y; }

struct IoSetup {
    IoSetup() {
        cin.tie(nullptr);
        ios::sync_with_stdio(false);
        cout << fixed << setprecision(10);
        cerr << fixed << setprecision(10);
    }
} iosetup;

template< typename T1, typename T2 >
ostream &operator << (ostream &os, const pair< T1, T2 > &p) {
    os << p.first << " " << p.second;
    return os;
}

template< typename T1, typename T2 >
istream &operator >> (istream &is, pair< T1, T2 > &p) {
    is >> p.first >> p.second;
    return is;
}

template< typename T1, typename T2, typename T3 >
ostream &operator << (ostream &os, const tuple< T1, T2, T3 > &t) {
    os << get<0>(t) << " " << get<1>(t) << " " << get<2>(t);
    return os;
}

template< typename T1, typename T2, typename T3 >
istream &operator >> (istream &is, tuple< T1, T2, T3 > &t) {
    is >> get<0>(t) >> get<1>(t) >> get<2>(t);
    return is;
}

template< typename T >
ostream &operator << (ostream &os, const vector< T > &v){
    for (int i = 0; i < (int)v.size(); ++i) {
        os << v[i] << (i + 1 != v.size() ? " " : "");
    }
    return os;
}

template< typename T >
istream &operator >>  (istream &is, vector< T > &v){
    for(T &in : v) is >> in;
    return is;
}

/*---------------------------------    Tools    ------------------------------------------*/
template< typename T >
vector<T> cumsum(const vector<T> &X){
    vector<T> res(X.size() + 1, 0);
    for(int i = 0; i < X.size(); ++i) res[i + 1] += res[i] + X[i];
    return res;
}

template< typename S, typename T, typename F>
pair<T, T> bisearch(S left, T right, F f) {
    while(abs(right - left) > 1){
        T mid = (right + left) / 2;
        if(f(mid)) right = mid;
        else left = mid;
    }
    return {left, right};
}

template< typename S, typename T, typename F>
double trisearch(S left, T right, F f, double precision = 1e-10){
    double low = left, high = right;
    while(high - low > precision){
        double mid_left = high / 3 + low * 2 / 3;
        double mid_right = high * 2 / 3 + low / 3;
        if(f(mid_left) >= f(mid_right)) low = mid_left;
        else high = mid_right;
    }
    return high;
}

//coordinate compression
template< typename T >
struct Compression {
    vector<T> cd;

    Compression() = default;

    Compression(const vector<T> &v){
        add(v);
    }

    Compression(const initializer_list<vector<T>> &v){
        for(auto &p : v) add(p);
    }

    void add(const vector<T> &v){
        copy(begin(v), end(v), back_inserter(cd));
    }

    void add(const T &x) {
        cd.emplace_back(x);
    }

    void build() {
        sort(begin(cd), end(cd));
        cd.erase(unique(begin(cd), end(cd)), end(cd));
    }

    vector<int> get(const vector<T> &v) const{
        vector<int> ret;
        transform(begin(v), end(v), back_inserter(ret), [&](const T &x) {
            return lower_bound(begin(cd), end(cd), x) - begin(cd);
        });
        return ret;
    }

    int get(const T &x) const {
        return lower_bound(begin(cd), end(cd), x) - begin(cd);
    }

    const T &operator[](int k) const{
        return cd[k];
    }
};

//オンラインで中央値をO(log N)で求める
template < typename T >
struct FloatingMedian {
    priority_queue<T> F;
    priority_queue<T, vector<T>, greater<>> B;
    T fsum, bsum;

    FloatingMedian() : fsum(T(0)), bsum(T(0)) {}

    void push(T val){
        if (F.empty()){
            F.push(val), fsum += val;
            return;
        }
        
        if (F.size() > B.size()){
            if (val >= F.top()) B.push(val), bsum += val;
            else{
                bsum += F.top(), fsum -= F.top();
                B.push(F.top()), F.pop();
                F.push(val), fsum += val;
            }
            return;
        }

        if (val <= B.top()) F.push(val), fsum += val;
        else{
            fsum += B.top(), bsum -= B.top();
            F.push(B.top()), B.pop();
            B.push(val), bsum += val;
        }
    }

    pair<T, T> getMedian(){
        if((F.size() + B.size()) % 2) return {F.top(), F.top()};
        return {F.top(), B.top()};
    }
};


/*------------------------------- Main Code Here -----------------------------------------*/

int main()
{
    ll N;
    cin >> N;
    vec A(N);
    cin >> A;
    rep(i, N) A[i] -= (i + 1);

    auto solve = [&](ll x) {
        ll sum = 0;
        rep(i, N) sum += abs(A[i] - x);
        return sum;
    };

    FloatingMedian<ll> fm;

    rep(i, N) fm.push(A[i]);

    print(solve(fm.getMedian().first));

    return 0;
}

Measured memory_bytes: 3572