#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
using ll = long long;
using vll = vector<ll>;
using pll = pair<ll, ll>;
#define sz(x) int(x.size())
const ll INF = 1'000'000'000'000'000'000LL;
struct line
{
double a;
double b;
};
double intersect(line A, line B)
{
return (B.b-A.b)/(A.a-B.a);
}
int main()
{
int N;
cin >> N;
int TS = N;
vector<pll> T;
T.push_back({0, 0});
for(int i = 1; i <= N; i++)
{
ll t;
cin >> t;
if(t <= T.back().first)
T.back().second++;
else
T.push_back({t, 1});
}
N = sz(T)-1;
vll suff(1+N, 0);
suff[0] = TS;
for(int i = 1; i <= N; i++) suff[i] = suff[i-1] - T[i].second;
vll dp(1+N, INF);
dp[0] = 0;
vector<line> L;
L.push_back(line{double(suff[0]), double(dp[0])});
// for(int i = 0; i <= N; i++) cerr << T[i].first << ' ' << T[i].second << ' ' << suff[i] << '\n';
for(int i = 1; i <= N; i++)
{
int lo = 0;
int hi = sz(L) - 1;
double x = T[i].first;
while(lo != hi)
{
int mid = (lo+hi)/2;
if(intersect(L[mid], L[mid+1]) <= x) ///!!!!!!!!
lo = mid+1;
else
hi = mid;
}
// if(i == 2)
// {
// cerr << "!!!\n";
// cerr << intersect(L[0], L[1]) << '\n';
// cerr << "x = " << x << '\n';
// }
dp[i] = ll(L[lo].a) * T[i].first + ll(L[lo].b);
// for(auto y: L) cerr << y.a << "/" << y.b << " ";
// cerr << '\n';
// cerr << "lo = " << lo << '\n';
// cerr << i << " : " << dp[i] << '\n';
if(i < N)
{
line new_line{double(suff[i]), double(dp[i])};
while(sz(L) >= 2 && intersect(L[sz(L)-2], L[sz(L)-1]) >= intersect(L[sz(L)-1], new_line)) //!!!!!!!!!!!
L.pop_back();
L.push_back(new_line);
}
}
cout << dp[N] << '\n';
}
