#include <cstdio>
#include <queue>
using namespace std;
int n;
long long h;
long long t;
priority_queue<long long> lower;
priority_queue<long long,vector<long long>,greater<long long> > upper;
inline void read(int& x) {
x = 0;
char ch = getchar_unlocked();
while (ch&16){ //this will break when ‘\n’ or ‘ ‘ is encountered
x = (x << 3) + (x << 1) + (ch&15);
ch = getchar_unlocked();
}
}
inline void read(long long& x) {
x = 0;
char ch = getchar_unlocked();
while (ch&16){ //this will break when ‘\n’ or ‘ ‘ is encountered
x = (x << 3) + (x << 1) + (ch&15);
ch = getchar_unlocked();
}
}
int main(){
read(n),read(h);
read(t);
lower.push(t);
upper.push(t);
long long ans=0;
long long offset;
for (int x=1;x<n;x++){
offset=x*h;
read(t);
if (!lower.empty() && t<lower.top()-offset){ ///lower part
ans+=(lower.top()-offset)-t;
lower.push(t+offset);
lower.push(t+offset);
upper.push(lower.top()-offset*2);
lower.pop();
}
else if (!upper.empty() && upper.top()+offset<t){ ///upper part
ans+=t-(upper.top()+offset);
upper.push(t-offset);
upper.push(t-offset);
lower.push(upper.top()+offset*2);
upper.pop();
}
else{
lower.push(t+offset);
upper.push(t-offset);
}
//printf("%lld %lld %lld\n",ans,lower.top()-offset,upper.top()+offset);
}
printf("%lld\n",ans);
}
