#import<bits/stdc++.h>
using namespace std;
typedef long long ll;
ll n,m,ans;
priority_queue <ll,vector<ll>,less<ll>> Q;
int main() {
cin >> n;
for(ll x=0; x<n; x++) {
cin >> m;
Q.push(m-x);
if(!Q.empty() && Q.top() > m-x) {
ans += Q.top()-m + x;
Q.pop();
Q.push(m-x);
}
}
cout<<ans;
}