import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		long[] a = new long[n];
		long steps = 0;
		long level;
		
		
		for(int i = 0; i < n; i++) {
			a[i] = sc.nextLong();
		}
		
		level = a[0];
		
		for(int i = 0; i < n -1; i++) {
			if(level > a[i + 1]) {
				steps += (level - a[i + 1]);
			} else {
				level = a[i + 1];
			}
		}
		
		System.out.println(steps);
	}

} import java.util.Scanner; Scanner 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];
		long steps = 0;
		long level;
		
		
		for(int i = 0; i < n; i++) {
			a[i] = sc.nextLong();
		}
		
		level = a[0];
		
		for(int i = 0; i < n -1; i++) {
			if(level > a[i + 1]) {
				steps += (level - a[i + 1]);
			} else {
				level = a[i + 1];
			}
		}
		
		System.out.println(steps);
	}

} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		long[] a = new long[n];
		long steps = 0;
		long level;
		
		
		for(int i = 0; i < n; i++) {
			a[i] = sc.nextLong();
		}
		
		level = a[0];
		
		for(int i = 0; i < n -1; i++) {
			if(level > a[i + 1]) {
				steps += (level - a[i + 1]);
			} else {
				level = a[i + 1];
			}
		}
		
		System.out.println(steps);
	} main {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		long[] a = new long[n];
		long steps = 0;
		long level;
		
		
		for(int i = 0; i < n; i++) {
			a[i] = sc.nextLong();
		}
		
		level = a[0];
		
		for(int i = 0; i < n -1; i++) {
			if(level > a[i + 1]) {
				steps += (level - a[i + 1]);
			} else {
				level = a[i + 1];
			}
		}
		
		System.out.println(steps);
	} 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 long steps = 0; steps 0 long level; level for(int i = 0; i < n; i++) {
			a[i] = sc.nextLong();
		} int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
			a[i] = sc.nextLong();
		} {
			a[i] = sc.nextLong();
		} a[i] = sc.nextLong() a[i] a i sc.nextLong() sc.nextLong sc level = a[0] level a[0] a 0 for(int i = 0; i < n -1; i++) {
			if(level > a[i + 1]) {
				steps += (level - a[i + 1]);
			} else {
				level = a[i + 1];
			}
		} int i = 0; int i = 0; i 0 i < n -1 i n -1 n 1 i++ i++ i {
			if(level > a[i + 1]) {
				steps += (level - a[i + 1]);
			} else {
				level = a[i + 1];
			}
		} {
			if(level > a[i + 1]) {
				steps += (level - a[i + 1]);
			} else {
				level = a[i + 1];
			}
		} if(level > a[i + 1]) {
				steps += (level - a[i + 1]);
			} else {
				level = a[i + 1];
			} level > a[i + 1] level a[i + 1] a i + 1 i 1 {
				steps += (level - a[i + 1]);
			} steps += (level - a[i + 1]) steps (level - a[i + 1]) level a[i + 1] a i + 1 i 1 {
				level = a[i + 1];
			} level = a[i + 1] level a[i + 1] a i + 1 i 1 System.out.println(steps) System.out.println System.out System System.out steps 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];
		long steps = 0;
		long level;
		
		
		for(int i = 0; i < n; i++) {
			a[i] = sc.nextLong();
		}
		
		level = a[0];
		
		for(int i = 0; i < n -1; i++) {
			if(level > a[i + 1]) {
				steps += (level - a[i + 1]);
			} else {
				level = a[i + 1];
			}
		}
		
		System.out.println(steps);
	}

} public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		long[] a = new long[n];
		long steps = 0;
		long level;
		
		
		for(int i = 0; i < n; i++) {
			a[i] = sc.nextLong();
		}
		
		level = a[0];
		
		for(int i = 0; i < n -1; i++) {
			if(level > a[i + 1]) {
				steps += (level - a[i + 1]);
			} else {
				level = a[i + 1];
			}
		}
		
		System.out.println(steps);
	}

} Main
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		long[] a = new long[n];
		long steps = 0;
		long level;
		
		
		for(int i = 0; i < n; i++) {
			a[i] = sc.nextLong();
		}
		
		level = a[0];
		
		for(int i = 0; i < n -1; i++) {
			if(level > a[i + 1]) {
				steps += (level - a[i + 1]);
			} else {
				level = a[i + 1];
			}
		}
		
		System.out.println(steps);
	}

}