import java.util.Scanner;

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

	}
} 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 [] height = new long[N];
		for(int i = 0; i < N ; i++) {
			height[i] = sc.nextLong();
		}
		long ans = 0;
		for(int i = 0; i < N-1; i++) {
			if(height[i] > height[i+1]) {
				long tmp = height[i]-height[i+1];
				ans += tmp;
				height[i+1]  += tmp;
			}
		}
		System.out.println(ans);

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

	} main {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		long [] height = new long[N];
		for(int i = 0; i < N ; i++) {
			height[i] = sc.nextLong();
		}
		long ans = 0;
		for(int i = 0; i < N-1; i++) {
			if(height[i] > height[i+1]) {
				long tmp = height[i]-height[i+1];
				ans += tmp;
				height[i+1]  += tmp;
			}
		}
		System.out.println(ans);

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

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

	}
} 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 [] height = new long[N];
		for(int i = 0; i < N ; i++) {
			height[i] = sc.nextLong();
		}
		long ans = 0;
		for(int i = 0; i < N-1; i++) {
			if(height[i] > height[i+1]) {
				long tmp = height[i]-height[i+1];
				ans += tmp;
				height[i+1]  += tmp;
			}
		}
		System.out.println(ans);

	}
}