import java.util.*;
public class Main {
	public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        long[] A = new long[N];
        for (int i=0; i<N; i++) {
            A[i] = sc.nextInt();
        }

        long top = 0;
        long result = 0;

        for (int i=0; i<N; i++) {
            if (A[i] > top) {
                top = A[i];
            } else if ((A[i] < top)) {
                result += (top-A[i]);
            }
        }
        
        System.out.println(result);
    }
} import java.util.*; util.* java public class Main {
	public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        long[] A = new long[N];
        for (int i=0; i<N; i++) {
            A[i] = sc.nextInt();
        }

        long top = 0;
        long result = 0;

        for (int i=0; i<N; i++) {
            if (A[i] > top) {
                top = A[i];
            } else if ((A[i] < top)) {
                result += (top-A[i]);
            }
        }
        
        System.out.println(result);
    }
} Main public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        long[] A = new long[N];
        for (int i=0; i<N; i++) {
            A[i] = sc.nextInt();
        }

        long top = 0;
        long result = 0;

        for (int i=0; i<N; i++) {
            if (A[i] > top) {
                top = A[i];
            } else if ((A[i] < top)) {
                result += (top-A[i]);
            }
        }
        
        System.out.println(result);
    } main {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        long[] A = new long[N];
        for (int i=0; i<N; i++) {
            A[i] = sc.nextInt();
        }

        long top = 0;
        long result = 0;

        for (int i=0; i<N; i++) {
            if (A[i] > top) {
                top = A[i];
            } else if ((A[i] < top)) {
                result += (top-A[i]);
            }
        }
        
        System.out.println(result);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int N = sc.nextInt(); N sc.nextInt() sc.nextInt sc long[] A = new long[N]; A new long[N] N for (int i=0; i<N; i++) {
            A[i] = sc.nextInt();
        } int i=0; int i=0; i 0 i<N i N i++ i++ i {
            A[i] = sc.nextInt();
        } {
            A[i] = sc.nextInt();
        } A[i] = sc.nextInt() A[i] A i sc.nextInt() sc.nextInt sc long top = 0; top 0 long result = 0; result 0 for (int i=0; i<N; i++) {
            if (A[i] > top) {
                top = A[i];
            } else if ((A[i] < top)) {
                result += (top-A[i]);
            }
        } int i=0; int i=0; i 0 i<N i N i++ i++ i {
            if (A[i] > top) {
                top = A[i];
            } else if ((A[i] < top)) {
                result += (top-A[i]);
            }
        } {
            if (A[i] > top) {
                top = A[i];
            } else if ((A[i] < top)) {
                result += (top-A[i]);
            }
        } if (A[i] > top) {
                top = A[i];
            } else if ((A[i] < top)) {
                result += (top-A[i]);
            } A[i] > top A[i] A i top {
                top = A[i];
            } top = A[i] top A[i] A i if ((A[i] < top)) {
                result += (top-A[i]);
            } (A[i] < top) A[i] A i top {
                result += (top-A[i]);
            } result += (top-A[i]) result (top-A[i]) top A[i] A i System.out.println(result) System.out.println System.out System System.out result String[] args args public class Main {
	public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        long[] A = new long[N];
        for (int i=0; i<N; i++) {
            A[i] = sc.nextInt();
        }

        long top = 0;
        long result = 0;

        for (int i=0; i<N; i++) {
            if (A[i] > top) {
                top = A[i];
            } else if ((A[i] < top)) {
                result += (top-A[i]);
            }
        }
        
        System.out.println(result);
    }
} public class Main {
	public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        long[] A = new long[N];
        for (int i=0; i<N; i++) {
            A[i] = sc.nextInt();
        }

        long top = 0;
        long result = 0;

        for (int i=0; i<N; i++) {
            if (A[i] > top) {
                top = A[i];
            } else if ((A[i] < top)) {
                result += (top-A[i]);
            }
        }
        
        System.out.println(result);
    }
} Main
import java.util.*;
public class Main {
	public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        long[] A = new long[N];
        for (int i=0; i<N; i++) {
            A[i] = sc.nextInt();
        }

        long top = 0;
        long result = 0;

        for (int i=0; i<N; i++) {
            if (A[i] > top) {
                top = A[i];
            } else if ((A[i] < top)) {
                result += (top-A[i]);
            }
        }
        
        System.out.println(result);
    }
}
