Increasing Array

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;
long long arr[200000];

int main() {
	//freopen("cases.txt", "r", stdin);
	int num;
	cin >> num;
	long long result = 0 ;

	if (num == 1) {
		cout << "0" << endl;
		return 0;
	}


	int first;
	int second;

	if (num == 2) {
		cin >> first >> second;
		if (second < first){
			cout << second - first << endl;
			return 0;
			}

		else{
			cout << "0" << endl;
			return 0;
			}
	}

	
	cin >> first;
	cin >> second;
	for (int i = 0; i < num - 1; i++) {
		if (second < first)
			result += first - second;
		first = second;
		cin >> second;
	}
	cout << result << endl;
	return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: WRONG ANSWER

Test 3

Verdict: WRONG ANSWER

Test 4

Verdict: ACCEPTED

Test 5

Verdict: WRONG ANSWER

Test 6

Verdict: WRONG ANSWER

Test 7

Verdict: ACCEPTED