/* * Author: Nonoze * Created: Saturday 20/12/2025 */ #include <bits/stdc++.h> using namespace std; #ifndef DEBUG #define dbg(...) #endif // #define cout cerr << "OUT: " #define endl '\n' #define endlfl '\n' << flush #define quit(x) return (void)(cout << x << endl) template<typename T> void read(T& x) { cin >> x; } template<typename T1, typename T2> void read(pair<T1, T2>& p) { read(p.first), read(p.second); } template<typename T> void read(vector<T>& v) { for (auto& x : v) read(x); } template<typename T1, typename T2> void read(T1& x, T2& y) { read(x), read(y); } template<typename T1, typename T2, typename T3> void read(T1& x, T2& y, T3& z) { read(x), read(y), read(z); } template<typename T1, typename T2, typename T3, typename T4> void read(T1& x, T2& y, T3& z, T4& zz) { read(x), read(y), read(z), read(zz); } template<typename T> void print(vector<T>& v) { for (auto& x : v) cout << x << ' '; cout << endl; } #define sz(x) (int)(x.size()) #define all(x) (x).begin(), (x).end() #define rall(x) (x).rbegin(), (x).rend() #define make_unique(v) sort(all(v)), v.erase(unique(all(v)), (v).end()) #define pb push_back #define mp(a, b) make_pair(a, b) #define fi first #define se second #define cmin(a, b) a = min(a, b) #define cmax(a, b) a = max(a, b) #define YES cout << "YES" << endl #define NO cout << "NO" << endl #define QYES quit("YES") #define QNO quit("NO") #define int long long #define double long double const int inf = numeric_limits<int>::max() / 4; mt19937 rng(chrono::steady_clock::now().time_since_epoch().count()); const int MOD = 1e9+7, LOG=20; void solve(); signed main() { ios::sync_with_stdio(0); cin.tie(0); int tt=1; // cin >> tt; while(tt--) solve(); return 0; } int n, k, m, q; vector<int> a; void solve() { read(n); a.clear(), a.resize(n); read(a); vector<int> b=a; for (int i=n-2; i>=0; i--) cmax(b[i], b[i+1]+1); int addedright=0, addedleft=0; for (int i=n-2; i>=0; i--) { int addact=b[i]-a[i], addprec=b[i+1]-a[i+1]; if (addprec>addact) { addedright+=addprec-addact; } } int ans=addedright+max(0LL, b[0]-a[0]); if (n>=2 && b[1]-a[1]>b[0]-a[0]) addedright-=b[1]-a[1]- (b[0]-a[0]); b[0]=a[0]; for (int i=1; i<n; i++) { if (i+1<n) { int addact=b[i]-a[i], addprec=b[i+1]-a[i+1]; if (addprec>addact) addedright-=addprec-addact; } cmax(b[i], b[i-1]+1); int right=0; if (i+1<n) right=max(0LL, b[i+1]-a[i+1]); int left=max(0LL, b[i-1]-a[i-1]); cmin(ans, max(addedleft+left, addedright+right) + max(0LL, b[i] - (a[i] + max(addedleft+left, addedright+right) - min(addedleft+left, addedright+right)) )); b[i]=max(a[i], b[i-1]+1); int addact=b[i]-a[i], addprec=b[i-1]-a[i-1]; if (addprec>addact) { addedleft+=addprec-addact; } } cout << ans << endl; }