#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp> 
#include <ext/pb_ds/detail/standard_policies.hpp>
using namespace __gnu_pbds;
using namespace std;
#define getbit(n, i) (((n) & (1LL << (i))) != 0) 
#define setbit0(n, i) ((n) & (~(1LL << (i)))) 
#define setbit1(n, i) ((n) | (1LL << (i))) 
#define togglebit(n, i) ((n) ^ (1LL << (i))) 
#define lastone(n) ((n) & (-(n))) 
char gap = 32;
#define ll long long 
#define int long long 
#define lll __int128_t
#define pb push_back
typedef tree<
int,
null_type,
less<int>,
rb_tree_tag,
tree_order_statistics_node_update>
ordered_set;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

void solve(){
    int n;
    cin>>n;
    int ara[n];
    for(int i=0;i<n;i++) cin>>ara[i];
    int res = 0;
    for(int i=1;i<n;i++){
        if( ara[i] > ara[i-1]){
            res += ara[i] - ara[i-1];
            ara[i] = ara[i-1];
        }
    }
    cout<<res<<endl;

}
signed main(){
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);

    solve();
    return 0;
}