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 ull unsigned long long int
#define ll long long
#define f(i,n) for(int i = 0;i<n ;i++)
#define ii pair<int,int>
#define vii vector<ii>
#define vi vector<int>
#define vl vector<ll>
#define mii map<int,int>
#define uii unordered_map<int,int>
#define all(x) x.begin(),x.end()
#define ff first
#define ss second
#define fast_io ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
#define endl "\n"
#define pb push_back
#define INF 0x3f3f3f3f
#define print(x) cout<<x<<"\n";
#define printv(v) for(auto it : v) cout<<it<<" ";


//#include<boost/multiprecision/cpp_int.hpp>
//#include<ext/pb_ds/assoc_container.hpp>
//#include<ext/pb_ds/tree_policy.hpp>
//(Uncomment when needed and be sure it not give TLE bcoz it requires time)
//#pragma GCC optimize "trapv"//to check integer overflow and gives RE.
//typedef tree<pair<int,int>,null_type, 
//less<pair<int,int>>,rb_tree_tag,tree_order_statistics_node_update>   ordered_set;
//(UNCOMMENT WHEN HAVING LOTS OF RECURSIONS)\
#pragma comment(linker, "/stack:200000000")
//(UNCOMMENT WHEN NEEDED)\
#pragma GCC optimize("Ofast,unroll-loops,no-stack-protector,fast-math")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
//#pragma GCC optimize("O3")
//uncoment for large int requirement
//using boost::multiprecision::cpp_int;
//using namespace _gnu_pbds;

using namespace std;
const long long int MOD = 1e9+7;
struct custom_hash {
    static uint64_t splitmix64(uint64_t x) {
        // http://xorshift.di.unimi.it/splitmix64.c
        x += 0x9e3779b97f4a7c15;
        x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
        x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
        return x ^ (x >> 31);
    }

    size_t operator()(uint64_t x) const {
        static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();
        return splitmix64(x + FIXED_RANDOM);
    }
};
//use it with unordered_map<T,T,custom_hash> safe_map

int dx[]={-1,0,1,0};
int dy[]={0,1,0,-1};

int main()
{fast_io

int t;
//cin>>t;
t = 1;
while(t--)
{
int n;
cin>>n;
vi v(n);
for(int i = 0 ;i<n ;i ++)
cin>>v[i];
ll sum = 0 ; 
int mx = v[0];
for(int i = 1;i<n ;i ++)
{
    sum+=(max(mx-v[i],0));
    mx = max(v[i],mx);
}
cout<<sum<<endl;

}
}