#include <bits/stdc++.h>
using namespace std;
#define rep(index,num) for(int index=0;index<num;index++)
#define rep1(index,num) for(int index=1;index<=num;index++)
#define brep(index,num) for(int index=num-1;index>=0;index--)
#define brep1(index,num) for(int index=num;index>0;index--)
#define prin(a) cout<<a<<"\n"
#define kaigyo cout<<"\n"
#define mp(a1,a2) make_pair(a1,a2)
#define ALL(a) (a).begin(),(a).end()
#define rALL(a) (a).rbegin(),(a).rend()
#define SORT(V) sort(ALL(V))
#define REV(V) reverse(ALL(V))
#define RSORT(V) SORT(V);REV(V)
#define mem(x) memset(x,0,sizeof(x))
#define mem1(x) memset(x,-1,sizeof(x))
typedef long long ll;
typedef long double ld;
typedef pair<ll,ll> pll;
typedef pair<int,int> pint;
typedef vector<int> vint;
typedef vector<ll> vll;
typedef vector<string> vst;
typedef vector<char> vc;
typedef vector<long double> vd;
typedef vector<pint> vpint;
typedef vector<pll> vpll;
typedef vector<vector<int>> vint2;
ll mod=1e9+7;
#define int1(x) int x;cin>>x;
#define int2(x,y) int x,y;cin>>x>>y;
#define int3(x,y,z) int x,y,z;cin>>x>>y>>z;
#define int4(x,y,z,w) int x,y,z,w;cin>>x>>y>>z>>w;
#define ll1(x) ll x;cin>>x;
#define ll2(x,y) ll x,y;cin>>x>>y;
#define vint1(a,n) vint a(n);rep(i,n)cin>>a[i];
#define vint2(a,b,n) vint a(n),b(n);rep(i,n)cin>>a[i]>>b[i];
#define vll1(a,n) vll a(n);rep(i,n)cin>>a[i];
struct aaa{
    aaa(){
        cin.tie(0); ios::sync_with_stdio(0); cout<<fixed<<setprecision(20);
    };
}aaaaaaa;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
#define F first
#define S second
const double pi=acos(-1.0);
const ll inf=1LL<<60;
// modint: mod 計算の構造体
/*template<int MOD> struct Fp {
    long long val;
    constexpr Fp(long long v = 0) noexcept : val(v % MOD) {
        if (val < 0) val += MOD;
    }
    constexpr int getmod() { return MOD; }
    constexpr Fp operator - () const noexcept {
        return val ? MOD - val : 0;
    }
    constexpr Fp operator + (const Fp& r) const noexcept { return Fp(*this) += r; }
    constexpr Fp operator - (const Fp& r) const noexcept { return Fp(*this) -= r; }
    constexpr Fp operator * (const Fp& r) const noexcept { return Fp(*this) *= r; }
    constexpr Fp operator / (const Fp& r) const noexcept { return Fp(*this) /= r; }
    constexpr Fp& operator += (const Fp& r) noexcept {
        val += r.val;
        if (val >= MOD) val -= MOD;
        return *this;
    }
    constexpr Fp& operator -= (const Fp& r) noexcept {
        val -= r.val;
        if (val < 0) val += MOD;
        return *this;
    }
    constexpr Fp& operator *= (const Fp& r) noexcept {
        val = val * r.val % MOD;
        return *this;
    }
    constexpr Fp& operator /= (const Fp& r) noexcept {
        long long a = r.val, b = MOD, u = 1, v = 0;
        while (b) {
            long long t = a / b;
            a -= t * b; swap(a, b);
            u -= t * v; swap(u, v);
        }
        val = val * u % MOD;
        if (val < 0) val += MOD;
        return *this;
    }
    constexpr bool operator == (const Fp& r) const noexcept {
        return this->val == r.val;
    }
    constexpr bool operator != (const Fp& r) const noexcept {
        return this->val != r.val;
    }
    friend constexpr ostream& operator << (ostream &os, const Fp<MOD>& x) noexcept {
        return os << x.val;
    }
    friend constexpr Fp<MOD> modpow(const Fp<MOD> &a, long long n) noexcept {
        if (n == 0) return 1;
        auto t = modpow(a, n / 2);
        t = t * t;
        if (n & 1) t = t * a;
        return t;
    }
};
const int MOD = 1000000007;
using mint = Fp<MOD>;*/



bool isPrime(ll n){if(n<2)return false;for(ll x = 2;
x*x <=n;x++){if(n%x == 0)return false;}return true;}
ll kaizyo(ll k){ll sum=1;rep1(i,k){sum*=i;sum%=mod;}return sum;}
ll ncr(ll n,ll r){return kaizyo(n)/(kaizyo(r)*kaizyo(n-r));}
unsigned keta(unsigned num){
    return log10(num)+1;
}


int main(){

int1(n);vint1(a,n);

ll humi=a[0],cnt=0;
rep(i,n){
    if(a[i]<humi)cnt+=humi-a[i];
    else{
        humi=a[i];
    }
}
prin(cnt);
}

Measured memory_bytes: 3988