#!/jcode/lang/cpp https://xitu.github.io/jcode-languages/dist/lang-cpp.json

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <set>
#include <map>
#include <unordered_map>
#include <unordered_set>

#define debug(a) cout << #a << " = " << a << endl;
#define debug2(a,b) cout<<#a<<" = "<<a<<' '<<#b<<" = "<<b<<endl;
#define debug3(a,b,c) cout<<#a<<" = "<<a<<' '<<#b<<" = "<<b<<' '<<#c<<" = "<<c<<endl;
#define debug4(a,b,c,d) cout<<#a<<" = "<<a<<' '<<#b<<" = "<<b<<' '<<#c<<" = "<<c<<' '<<#d<<" = "<<d<<endl;
#define debug5(a,b,c,d,e) cout<<#a<<" = "<<a<<' '<<#b<<" = "<<b<<' '<<#c<<" = "<<c<<' '<<#d<<" = "<<d<<' '<<#e<<" = "<<e<<endl;
#define debugx(a, idx) cout << #a << "[" << idx << "] = " << a[idx] << endl;
#define debugarr(a, x) for(int i = 0; i < x; i++) cout << a[i] << ' '; cout << endl;
#define debugvec(a) for(int i = 0; i < a.size(); i++) cout << a[i] << ' '; cout << endl;
#define debugarr2(a, n, m) cout<<#a<<": \n";for(int i=0;i<n;i++){for(int j=0;j<m;j++)cout<<a[i][j]<<' ';cout<<'\n';}

#define pb push_back
#define mk make_pair
#define rep(i, a, n) for(int i=a;i<n;i++)
#define per(i, a, n) for(int i=n-1;i>=a;i--)
#define all(x) (x).begin(), (x).end()
#define vc vector
#define fi first
#define se second
#define SZ(X) ((int)(X).size())
using namespace std;
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using piii = pair<int, pair<int, int>>;
const int inf = 0x3f3f3f3f;
const ll inff = 0x3f3f3f3f3f3f3f3f;
const ll mod = 1e9 + 7;
const int N = 3e6+10;


void slove(){
    int n; cin >> n;
    vc<int> v(n);
    for(int i = 0; i < n; i ++) cin >> v[i];

    vc<int> pre(n), hou(n);
    pre[0] = v[0]; hou[n-1] = v[n-1];
    for(int i = 1; i < n; i ++) pre[i] = max(pre[i-1], v[i]);
    for(int i = n-2; i >= 0; i --) hou[i] = max(hou[i+1], v[i]);

    int ans = 0;
    for(int i = 1; i < n-1; i ++){
        ans += min(pre[i], hou[i]) - v[i];
    }

    cout << ans << '\n';
}


int main(){
    // #ifndef ONLINE_JUDGE
    //     freopen("in.txt", "r", stdin);
    //     freopen("out.txt", "w", stdout);
    // #endif
    ios::sync_with_stdio(false); cin.tie(0); cout.tie(0);

    // int tt; cin >> tt;
    // while(tt --)
        slove();

    // #ifndef ONLINE_JUDGE
    //     cout << "Time used = " << (double)clock() / CLOCKS_PER_SEC << " (s)" << endl;
    // #endif
    return 0;
}