#ifndef LOCAL
#define FAST_IO
#endif
// ============
#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <charconv>
#include <cmath>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
#define OVERRIDE(a, b, c, d, ...) d
#define REP2(i, n) for (i32 i = 0; i < (i32)(n); ++i)
#define REP3(i, m, n) for (i32 i = (i32)(m); i < (i32)(n); ++i)
#define REP(...) OVERRIDE(__VA_ARGS__, REP3, REP2)(__VA_ARGS__)
#define PER(i, n) for (i32 i = (i32)(n) - 1; i >= 0; --i)
#define ALL(x) begin(x), end(x)
using namespace std;
using u32 = unsigned int;
using u64 = unsigned long long;
using i32 = signed int;
using i64 = signed long long;
using f64 = double;
using f80 = long double;
template <typename T>
using Vec = vector<T>;
template <typename T>
bool chmin(T &x, const T &y) {
if (x > y) {
x = y;
return true;
}
return false;
}
template <typename T>
bool chmax(T &x, const T &y) {
if (x < y) {
x = y;
return true;
}
return false;
}
#ifdef INT128
using u128 = __uint128_t;
using i128 = __int128_t;
istream &operator>>(istream &is, i128 &x) {
i64 v;
is >> v;
x = v;
return is;
}
ostream &operator<<(ostream &os, i128 x) {
os << (i64)x;
return os;
}
istream &operator>>(istream &is, u128 &x) {
u64 v;
is >> v;
x = v;
return is;
}
ostream &operator<<(ostream &os, u128 x) {
os << (u64)x;
return os;
}
#endif
[[maybe_unused]] constexpr i32 INF = 1000000100;
[[maybe_unused]] constexpr i64 INF64 = 3000000000000000100;
struct SetUpIO {
SetUpIO() {
#ifdef FAST_IO
ios::sync_with_stdio(false);
cin.tie(nullptr);
#endif
cout << fixed << setprecision(15);
}
} set_up_io;
// ============
#ifdef DEBUGF
#else
#define DBG(x) (void)0
#endif
class CHT {
struct Line {
i64 a, b;
i64 operator()(i64 x) const {
return a * x + b;
}
};
static i64 inter(Line l0, Line l1) {
assert(l0.a > l1.a);
i64 ret = (l1.b - l0.b) / (l0.a - l1.a);
/*if (l1.b - l0.b < 0 && (l1.b - l0.b) % (l0.a - l1.a) != 0) {
ret -= 1;
}*/
return ret;
}
deque<Line> lines;
public:
CHT() : lines() {}
void add(i64 a, i64 b) {
if (!lines.empty() && lines.back().a == a) {
if (lines.back().b > b) {
lines.pop_back();
} else {
return;
}
}
if (!lines.empty()) {
assert(lines.back().a > a);
}
Line line{a, b};
while (lines.size() >= 2 && inter(lines[lines.size() - 2], lines.back()) >= inter(lines.back(), line)) {
lines.pop_back();
}
lines.push_back(line);
}
i64 get(i64 x) {
assert(!lines.empty());
while (lines.size() >= 2 && lines[0](x) > lines[1](x)) {
lines.pop_front();
}
return lines.front()(x);
}
};
int main() {
i32 n;
cin >> n;
Vec<i64> t(n);
REP(i, n) {
cin >> t[i];
}
REP(i, n - 1) {
chmax(t[i + 1], t[i]);
}
reverse(ALL(t));
Vec<i64> dp(n + 1, 0);
CHT cht;
REP(i, n) {
cht.add(t[i], dp[i]);
dp[i + 1] = cht.get(i + 1);
}
cout << dp[n] << '\n';
}
