#include <bits/stdc++.h>
using namespace std;
#define ar array
#define ll long long
const int MAX_N = 1e5 + 1;
const ll MOD = 1e9 + 7;
const ll INF = 1e9;
struct convexhull {
struct line {
ll m, c;
line(ll m, ll c): m(m), c(c) {}
ll operator()(ll x) {return m * x + c;}
};
deque<line> dq;
bool bad(line a, line b, line c) {
return 1.0 * (c.c - a.c) / (a.m - c.m) <= 1.0 * (b.c - a.c) / (a.m - b.m);
}
void add(line l) {
while(dq.size() > 1 && bad(dq[(int)dq.size() - 2], dq.back(), l))
dq.pop_back();
dq.emplace_back(l);
}
long query(long x) {
if(dq.empty()) return 1e18;
int l = 0, r = (int)dq.size() - 1;
while(l < r) {
int mid = (l + r) >> 1;
if(dq[mid](x) >= dq[mid + 1](x))
l = mid + 1;
else r = mid;
}
return dq[r](x);
}
};
void solve() {
int n; cin >> n;
vector<int> a(n + 1);
for (int i = n; i > 0; i--) cin >> a[i];
vector<int> st;
for (int i = 1; i <= n; i++) {
while (st.size() && a[st.back()] <= a[i]) st.pop_back();
st.push_back(i);
}
int m = st.size();
vector<ll> dp(m + 1);
convexhull cht;
for (int i = 1; i <= m; i++) {
cht.add({a[st[i - 1]], dp[i - 1]});
dp[i] = cht.query(st[i - 1]);
}
cout << dp[m] << "\n";
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
int tc = 1;
// cin >> tc;
for (int t = 1; t <= tc; t++) {
// cout << "Case #" << t << ": ";
solve();
}
}
