ok啊，深呼吸，头晕是正常的

#include <bits/stdc++.h>
using namespace std;

const int MAXN = 999999;

int main() {
    int n, ans = 0;
    cin >> n;

    int a[MAXN];
    for (int i = 1; i <= n; i++) {
        cin >> a[i];
    }

    int d[MAXN];
    for (int i = 1; i <= n; i++) {
        d[i] = a[i] - a[i - 1];
        if (d[i] >= 0) {
            ans += d[i];
        } else {
            continue;
        }
    }

    cout << ans;
    return 0;
}