#include "bits/stdc++.h"
#pragma GCC optimize("Ofast")

// Begin Header {{{
using namespace std;

#ifndef DEBUG
#define dump(...)
#endif

#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define rep(i, n) for (intmax_t i = 0, i##_limit = (n); i < i##_limit; ++i)
#define reps(i, b, e) for (intmax_t i = (b), i##_limit = (e); i <= i##_limit; ++i)
#define repr(i, b, e) for (intmax_t i = (b), i##_limit = (e); i >= i##_limit; --i)
#define var(Type, ...) Type __VA_ARGS__; input(__VA_ARGS__)

constexpr size_t operator""_zu(unsigned long long value) { return value; };
constexpr intmax_t operator""_jd(unsigned long long value) { return value; };
constexpr uintmax_t operator""_ju(unsigned long long value) { return value; };

constexpr int INF = 0x3f3f3f3f;
constexpr intmax_t LINF = 0x3f3f3f3f3f3f3f3f_jd;

namespace moke {

    template <class T> using MaxHeap = priority_queue<T, vector<T>, less<T>>;
    template <class T> using MinHeap = priority_queue<T, vector<T>, greater<T>>;

    inline void input() {}
    template <class Head, class... Tail> inline void input(Head&& head, Tail&&... tail) {
        cin >> head;
        input(forward<Tail>(tail)...);
    }

    template <class T> inline void input(vector<T> &vec) {
        for (auto &e: vec) {
            cin >> e;
        }
    }

    template <class T> inline void input(vector<vector<T>> &mat) {
        for (auto &vec: mat) {
            input(vec);
        }
    }

    inline void print() { cout << "\n"; }
    template <class Head, class... Tail> inline void print(Head&& head, Tail&&... tail) {
        static constexpr const char *delim[] = {"", " "};
        cout << head << delim[sizeof...(tail)];
        print(forward<Tail>(tail)...);
    }

    template <class T> inline ostream& operator<<(ostream &strm, const vector<T> &vec) {
        static constexpr const char *delim[] = {" ", ""};
        for (const auto &e: vec) {
            strm << e << delim[&e == &vec.back()];
        }
        return strm;
    }

    template <class T> inline vector<T> make_v(const T &initValue, size_t sz) {
        return vector<T>(sz, initValue);
    }

    template <class T, class... Args> inline auto make_v(const T &initValue, size_t sz, Args... args) {
        return vector<decltype(make_v<T>(initValue, args...))>(sz, make_v<T>(initValue, args...));
    }

    template <class A, class B> inline bool chmax(A &a, const B &b) noexcept {
        return b > a && (a = b, true);
    }

    template <class A, class B> inline bool chmin(A &a, const B &b) noexcept {
        return b < a && (a = b, true);
    }

    template <class A, class B> inline common_type_t<A, B> min(const A &a, const B &b) noexcept {
        return a < b ? a : b;
    }

    template <class A, class B, class... Args> inline common_type_t<A, B, Args...> min(const A &a, const B &b, const Args&... args) noexcept {
        return moke::min(a < b ? a : b, args...);
    }

    template <class A, class B> inline common_type_t<A, B> max(const A &a, const B &b) noexcept {
        return a > b ? a : b;
    }

    template <class A, class B, class... Args> inline common_type_t<A, B, Args...> max(const A &a, const B &b, const Args&... args) noexcept {
        return moke::max(a > b ? a : b, args...);
    }

    template <class A, class B> inline common_type_t<A, B> diff(const A &a, const B &b) noexcept {
        return a < b ? b - a : a - b;
    }

} // namespace moke

// }}} End Header

namespace moke {

    int main_() {
        ios_base::sync_with_stdio(false);
        cin.tie(nullptr);

        var(size_t, N);

        vector<intmax_t> a(N);
        input(a);

        vector<intmax_t> b(N);
        rep(i, N) {
            b[i] = a[i] - (i + 1);
        }

        sort(all(b));

        intmax_t b1 = b[N / 2], b2 = b[N / 2 - 1];

        intmax_t res1 = 0, res2 = 0;
        rep(i, N) {
            res1 += abs(a[i] - (b1 + (i + 1)));
            res2 += abs(a[i] - (b2 + (i + 1)));
        }

        print(min(res1, res2));

        return 0;
    }

} // namespace moke

// {{{
signed main() {
    moke::main_();
    return 0;
}
// }}}


Measured memory_bytes: 3328