#include <iostream>
#include <vector>
#include <algorithm>
 
using namespace std;
 
int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
 
    int n;
    cin >> n;
    vector<int> a(n);
 
    // Nhập độ cao
    for (int i = 0; i < n; i++) {
        cin >> a[i];
    }
 
    // Tính tổng lượng nước đọng
    long long ans = 0;
    for (int i = 0; i < n; i++) {
        // Tìm max_left và max_right
        int max_left = 0, max_right = 0;
 
        for (int j = 0; j <= i; j++) {
            max_left = max(max_left, a[j]);
        }
 
        for (int j = i; j < n; j++) {
            max_right = max(max_right, a[j]);
        }
 
        // Tính nước đọng tại vị trí i
        ans += max(0, min(max_left, max_right) - a[i]);
    }
 
    cout << ans << '\n';
    return 0;
}

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