Problem:
Score : 300 points

Problem Statement

N persons are standing in a row. The height of the i-th person from the front is A_i.

We want to have each person stand on a stool of some heights - at least zero - so that the following condition is satisfied for every person:

Condition: Nobody in front of the person is taller than the person. Here, the height of a person includes the stool.

Find the minimum total height of the stools needed to meet this goal.

Constraints

1 \leq N \leq 2\times 10^5

1 \leq A_i \leq 10^9

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
A_1 \ldots A_N

Output

Print the minimum total height of the stools needed to meet the goal.

Sample Input 1

5
2 1 5 4 3

Sample Output 1

4

If the persons stand on stools of heights 0, 1, 0, 1, and 2, respectively, their heights will be 2, 2, 5, 5, and 5, satisfying the condition.

We cannot meet the goal with a smaller total height of the stools.

Sample Input 2

5
3 3 3 3 3

Sample Output 2

0

Giving a stool of height 0 to everyone will work.

Solution in C++ (GCC 9.2.1) (judge verdict: Accepted)

#include"bits/stdc++.h"
#define fastio ios_base::sync_with_stdio(false)
#define ll long long int
#define ld long double
#define ict int t; cin >> t
#define lct ll t; cin >> t;
#define in(a) int a; cin >> a
#define ln(a) ll a; cin >> a
#define loop(i,n) for (ll i = 0; i < n; ++i) 
#define looprev(i,n) for (ll i=n-1; i>=0 ; --i)
#define LOOP(i,k,n) for (ll i = k; i <= n; ++i) 
#define LOOPREV(i,k,n) for (ll i = k; i >= n; --i) 
#define mp make_pair 
#define pa pair <ll,ll>
#define vec vector<ll>
#define vecpa vector<pa>
#define vec2D vector <ll<ll>>
#define que queue<ll>
#define deq deque<ll> 
#define stk stack<ll>
#define iterate vector<ll>::iterator
#define pub push_back
#define pob pop_back
#define pof pop_front
#define puf push_front
#define emp emplace_back
#define all(a) a.begin(),a.end();

using namespace std;

void solve(){
    ll n;
    cin >> n;
    vec a(n);
    loop(i,n) cin >> a[i];
    ll res = 0;
    for(ll i = 0 ; i<n-1 ; i++){
        if(a[i]> a[i+1]) {
            res += a[i]-a[i+1];
            a[i+1] = a[i]; 
        }
    }
    cout << res << endl;
}

int main()
{
    fastio;
    cin.tie(NULL);
    cout.tie(NULL);
    solve();
}