Problem:
Score : 400 points

Problem Statement

One day, Snuke was given a permutation of length N, a_1, a_2, ..., a_N, from his friend.

Find the following:

Constraints

1 ≦ N ≦ 200,000

(a_1, a_2, ..., a_N) is a permutation of (1, 2, ..., N).

Input

The input is given from Standard Input in the following format:

N
a_1 a_2 ... a_N

Output

Print the answer.

Note that the answer may not fit into a 32-bit integer.

Sample Input 1

3
2 1 3

Sample Output 1

9

Sample Input 2

4
1 3 2 4

Sample Output 2

19

Sample Input 3

8
5 4 8 1 2 6 7 3

Sample Output 3

85

Solution in C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for (int (i)=(0);(i)<(int)(n);++(i))
using ll = long long;
using P = pair<int, int>;
using namespace std;

template<class T> void vin(vector<T>& v, int n) {
    v.resize(n);
    for (int i = 0; i < n; ++i) {
        cin >> v[i];
    }
}

ll ind[200100];

int main() {
    ll N;
    cin >> N;
    rep(i, N) {
        ll a;
        cin >> a;
        ind[a] = i;
    }
    set<ll> st;
    st.insert(-1);
    st.insert(N);
    ll ans = 0;
    for (ll i=1; i<=N; ++i) {
        st.insert(ind[i]);
        ll l = *(--st.find(ind[i]));
        ll r = *(++st.find(ind[i]));
        //cout << ind[i] << " " << l << ", " << ind[r] << " " << r << endl;
        ans += i * (ind[i]-l) * (r-ind[i]);
    }
    cout << ans << endl;
    return 0;
}