import java.util.*;
import java.math.BigInteger;
// warm-up
public class Main {

	static void solve() {
		Scanner sc = new Scanner(System.in);
		int noc=sc.nextInt(), i=0, n=noc;
		BigInteger t = BigInteger.ZERO;
		int[] a = new int[noc];
		while (noc-->0) a[i++] = sc.nextInt();
		for (i=0; i<n-1; i++) {
			if (a[i]>a[i+1]) {
				t = t.add(new BigInteger(""+(a[i]-a[i+1])));
				a[i+1]=a[i];
			}
		}
		System.out.println(t);
		sc.close();		
	}

	public static void main(String args[]) {
		solve();
	}

} import java.util.*; util.* java import java.math.BigInteger; BigInteger java.math public class Main {

	static void solve() {
		Scanner sc = new Scanner(System.in);
		int noc=sc.nextInt(), i=0, n=noc;
		BigInteger t = BigInteger.ZERO;
		int[] a = new int[noc];
		while (noc-->0) a[i++] = sc.nextInt();
		for (i=0; i<n-1; i++) {
			if (a[i]>a[i+1]) {
				t = t.add(new BigInteger(""+(a[i]-a[i+1])));
				a[i+1]=a[i];
			}
		}
		System.out.println(t);
		sc.close();		
	}

	public static void main(String args[]) {
		solve();
	}

} Main static void solve() {
		Scanner sc = new Scanner(System.in);
		int noc=sc.nextInt(), i=0, n=noc;
		BigInteger t = BigInteger.ZERO;
		int[] a = new int[noc];
		while (noc-->0) a[i++] = sc.nextInt();
		for (i=0; i<n-1; i++) {
			if (a[i]>a[i+1]) {
				t = t.add(new BigInteger(""+(a[i]-a[i+1])));
				a[i+1]=a[i];
			}
		}
		System.out.println(t);
		sc.close();		
	} solve {
		Scanner sc = new Scanner(System.in);
		int noc=sc.nextInt(), i=0, n=noc;
		BigInteger t = BigInteger.ZERO;
		int[] a = new int[noc];
		while (noc-->0) a[i++] = sc.nextInt();
		for (i=0; i<n-1; i++) {
			if (a[i]>a[i+1]) {
				t = t.add(new BigInteger(""+(a[i]-a[i+1])));
				a[i+1]=a[i];
			}
		}
		System.out.println(t);
		sc.close();		
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int noc=sc.nextInt() noc sc.nextInt() sc.nextInt sc i=0 i 0 n=noc; n noc BigInteger t = BigInteger.ZERO; t BigInteger.ZERO BigInteger BigInteger.ZERO int[] a = new int[noc]; a new int[noc] noc while (noc-->0) a[i++] = sc.nextInt(); noc-->0 noc-- noc 0 a[i++] = sc.nextInt() a[i++] a i++ i sc.nextInt() sc.nextInt sc for (i=0; i<n-1; i++) {
			if (a[i]>a[i+1]) {
				t = t.add(new BigInteger(""+(a[i]-a[i+1])));
				a[i+1]=a[i];
			}
		} i=0; i=0 i 0 i<n-1 i n-1 n 1 i++ i++ i {
			if (a[i]>a[i+1]) {
				t = t.add(new BigInteger(""+(a[i]-a[i+1])));
				a[i+1]=a[i];
			}
		} {
			if (a[i]>a[i+1]) {
				t = t.add(new BigInteger(""+(a[i]-a[i+1])));
				a[i+1]=a[i];
			}
		} if (a[i]>a[i+1]) {
				t = t.add(new BigInteger(""+(a[i]-a[i+1])));
				a[i+1]=a[i];
			} a[i]>a[i+1] a[i] a i a[i+1] a i+1 i 1 {
				t = t.add(new BigInteger(""+(a[i]-a[i+1])));
				a[i+1]=a[i];
			} t = t.add(new BigInteger(""+(a[i]-a[i+1]))) t t.add(new BigInteger(""+(a[i]-a[i+1]))) t.add t new BigInteger(""+(a[i]-a[i+1])) a[i+1]=a[i] a[i+1] a i+1 i 1 a[i] a i System.out.println(t) System.out.println System.out System System.out t sc.close() sc.close sc public static void main(String args[]) {
		solve();
	} main {
		solve();
	} solve() solve String args[] args public class Main {

	static void solve() {
		Scanner sc = new Scanner(System.in);
		int noc=sc.nextInt(), i=0, n=noc;
		BigInteger t = BigInteger.ZERO;
		int[] a = new int[noc];
		while (noc-->0) a[i++] = sc.nextInt();
		for (i=0; i<n-1; i++) {
			if (a[i]>a[i+1]) {
				t = t.add(new BigInteger(""+(a[i]-a[i+1])));
				a[i+1]=a[i];
			}
		}
		System.out.println(t);
		sc.close();		
	}

	public static void main(String args[]) {
		solve();
	}

} public class Main {

	static void solve() {
		Scanner sc = new Scanner(System.in);
		int noc=sc.nextInt(), i=0, n=noc;
		BigInteger t = BigInteger.ZERO;
		int[] a = new int[noc];
		while (noc-->0) a[i++] = sc.nextInt();
		for (i=0; i<n-1; i++) {
			if (a[i]>a[i+1]) {
				t = t.add(new BigInteger(""+(a[i]-a[i+1])));
				a[i+1]=a[i];
			}
		}
		System.out.println(t);
		sc.close();		
	}

	public static void main(String args[]) {
		solve();
	}

} Main
import java.util.*;
import java.math.BigInteger;
// warm-up
public class Main {

	static void solve() {
		Scanner sc = new Scanner(System.in);
		int noc=sc.nextInt(), i=0, n=noc;
		BigInteger t = BigInteger.ZERO;
		int[] a = new int[noc];
		while (noc-->0) a[i++] = sc.nextInt();
		for (i=0; i<n-1; i++) {
			if (a[i]>a[i+1]) {
				t = t.add(new BigInteger(""+(a[i]-a[i+1])));
				a[i+1]=a[i];
			}
		}
		System.out.println(t);
		sc.close();		
	}

	public static void main(String args[]) {
		solve();
	}

}
