110. 数蝌蚪

n, k = map(int, input().split())
L = [int(i) for i in input().split()]
for i in range(n):
    L[i] -= k*i
L.sort()
if n%2:
    target = L[n//2]
else:
    target = (L[n//2]+L[n//2-1])//2
if target < 0:
    target = 0
res = 0
for i in range(n):
    res += abs(L[i]-target)
print(res)

#include <array>
#include <cstdint>
#include <iostream>
array<uint32_t, 300001> tadpoles;
int main() {
    uint32_t n, k; std::cin >> n >> k;
    for (uint32_t i = 0; i < n; ++i)
        std::cin >> tadpoles[i];
    uint32_t lo = 0, hi = 10001;
    while (lo != hi) {
        uint32_t mid = lo + (hi - lo) / 2, standard = mid;
                uint32_t lower = 0, higher = 0, exact = 0;
        for (uint32_t i = 0; i < n; ++i, standard += k)
            if (tadpoles[i] == standard)
                ++exact;
            else if (tadpoles[i] < standard)
                ++lower;
            else
                ++higher;
        if (exact + higher < lower) {
            hi = mid;
        } else if (exact + lower < higher) {
            lo = mid + 1;
        } else {
            lo = hi = mid;
            break;
        }
    }
    uint64_t cost = 0;
    auto standard = lo;
    for (u32 i = 0; i < n; ++i, standard += k)
        if (tadpoles[i] < standard)
            cost += standard - tadpoles[i];
        else
            cost += tadpoles[i] - standard;
    std::cout << cost << '\n';
}

#include<cstdio>
#include<cctype>
#include<cmath>
#include<cstring>
#include<algorithm>
#include<iostream>
using namespace std;


long long sub[300001];
int main()
{
#ifdef debug
    freopen("testdata.in", "r", stdin);
    freopen("testdata.out", "w", stdout);
#endif
    int n, k, b;
    long long result = 0, a = 0;
    scanf("%d%d", &n, &k);
    for(int i = 0; i < n; i++)
    {
        scanf("%d", &b);
        sub[i] = b - a;
        a += k;
    }
    sort(sub, sub + n);
    if(sub[n/2] <= 0)
    {
        int temp = sub[n/2];
        for(int i = 0; i < n; i++) sub[i] += temp;
    }
    for(int i = 0; i < n; i++) result += sub[i];
    printf("%lld\n", result);
    return 0;
}