CSES – Increasing Array

#include<bits/stdc++.h>
#define int long long
#define pii pair<int,int>
#define f first
#define s second
#define fastio ios_base::sync_with_stdio(0);cin.tie(0)
using namespace std;
//declare
int n;
vector<int> v;
//
signed main(){
    fastio;
    cin>>n;
    for(int i=0;i<n;i++){
        int x; cin>>x;
        v.push_back(x);
    }
    int ans = 0;
    for(int i=1;i<n;i++){
        if(v[i] < v[i-1]){
            ans += v[i-1] - v[i];
            v[i] = v[i-1];
        }
    }
    cout<<ans<<"\n";
    return 0;
}