#include <iostream>
#include <assert.h>
#include <algorithm>
#include <vector>
#define forn(i,n) for(int i=0;i<(int)n;++i)
#define fort(i,n) for(int i=0;i<=(int)n;++i)
#define fori(i,a,n) for(int i=a;i<(int)n;++i)
#define forit(i,a,n) for(int i=a;i<=(int)n;++i)
#define ALL(v) v.begin(),v.end()
#define SZ(v) (int)v.size()
using namespace std;
template<typename T>
ostream &operator<<(ostream &os, vector<T> v){
os<<"[";
forn(i,SZ(v)){
if(i) os<<", ";
os<<v[i];
}
os<<"]";
return os;
}
typedef long long ll;
const ll INF = 1000000000000000000;
struct Node{
ll ops = 0;
int act = 0, val = 0;
};
vector<Node> get(const vector<int> &a){
int n = SZ(a);
vector<Node> ret(n + 1);
int active = 0, last = 0;
forn(i,n){
int need = max(0, last - a[i] + 1);
ll ops = ret[i].ops + max(0, need - active);
active = need;
last = a[i]+need;
ret[i+1] = {ops, active, last};
}
return ret;
}
void solve(){
int n;
cin>>n;
vector<int> a(n);
for(int &x: a) cin>>x;
vector<Node> fromLeft, fromRight;
forn(_,2){
fromLeft = get(a);
swap(fromLeft, fromRight);
reverse(ALL(a));
}
reverse(ALL(fromRight));
//~ forn(_,2){
//~ fort(i,n){
//~ cerr<<"("<<fromLeft[i].ops<<","<<fromLeft[i].act<<","<<fromLeft[i].val<<")"<<"\t";
//~ }
//~ cerr<<endl;
//~ swap(fromLeft, fromRight);
//~ }
ll ans = INF;
forn(i,n){ // pone este valor como central
ll aux = fromLeft[i].ops + fromRight[i+1].ops; // operaciones iniciales
int val = max(fromLeft[i].val, fromRight[i+1].val)+1; // valor mínimo que debo tener
int minAct = min(fromLeft[i].act, fromRight[i+1].act); // cuanto me puedo ahorrar
int maxAct = max(fromLeft[i].act, fromRight[i+1].act); // cuanto puedo aprovechar
aux -= minAct;
int cur = a[i] + maxAct; // crezco lo mas que puedo
aux += max(0,val-cur);
ans = min(ans, aux);
}
cout<<ans<<"\n";
}
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
#ifdef LOCAL
freopen("A.in", "r", stdin);
int tcs;
cin>>tcs;
while(tcs--)
#endif
solve();
return 0;
}
