#include <bits/stdc++.h>
#define Loop(x,l,r) for (ll x = (l); x < (ll)(r); ++x)
#define LoopR(x,l,r) for (ll x = (r)-1; x >= (ll)(l); --x)
typedef long long ll;
typedef std::pair<int, int> pii;
typedef std::pair<ll , ll > pll;
using namespace std;
const int N = 200'010;
int fen[N];
void up(int i, int x)
{
++i;
while (i < N) {
fen[i] = min(fen[i], x);
i += i & -i;
}
}
int get(int r)
{
int ans = N;
while (r) {
ans = min(ans, fen[r]);
r -= r & -r;
}
return ans;
}
int dp[N];
int main()
{
cin.tie(0) -> sync_with_stdio(false);
int n, jmp;
cin >> n >> jmp;
vector<pii> vec;
vec.push_back({-jmp*(n+1), ~(n+1)});
Loop (i,1,n+1) {
int x;
cin >> x;
if (x-jmp*i <= 0)
vec.push_back({x-jmp*i, ~i});
}
sort(vec.begin(), vec.end());
reverse(vec.begin(), vec.end());
fill(dp, dp+N, N);
fill(fen, fen+N, N);
dp[0] = 0;
up(0, 0);
for (auto [_, i] : vec) {
i = ~i;
dp[i] = get(i) + i - 1;
up(i, dp[i] - i);
}
cout << dp[n+1] << '\n';
}
