import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] a = new int[n + 1];
		int[] b = new int[n];
		long count = 0;
		for (int i = 0; i < n + 1; i++) {
			a[i]=sc.nextInt();
		}
		for (int i = 0; i < n; i++) {
			b[i]=sc.nextInt();
		}
		for (int i = 0; i < n; i++) {
			int sub = Math.min(a[i],b[i]);
			b[i]-=sub;
			count += sub;
			sub = Math.min(a[i+1], b[i]);
			count += sub;
			a[i+1]-=sub;

		}
		System.out.println(count);
	}
} 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();
		int[] a = new int[n + 1];
		int[] b = new int[n];
		long count = 0;
		for (int i = 0; i < n + 1; i++) {
			a[i]=sc.nextInt();
		}
		for (int i = 0; i < n; i++) {
			b[i]=sc.nextInt();
		}
		for (int i = 0; i < n; i++) {
			int sub = Math.min(a[i],b[i]);
			b[i]-=sub;
			count += sub;
			sub = Math.min(a[i+1], b[i]);
			count += sub;
			a[i+1]-=sub;

		}
		System.out.println(count);
	}
} Main public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] a = new int[n + 1];
		int[] b = new int[n];
		long count = 0;
		for (int i = 0; i < n + 1; i++) {
			a[i]=sc.nextInt();
		}
		for (int i = 0; i < n; i++) {
			b[i]=sc.nextInt();
		}
		for (int i = 0; i < n; i++) {
			int sub = Math.min(a[i],b[i]);
			b[i]-=sub;
			count += sub;
			sub = Math.min(a[i+1], b[i]);
			count += sub;
			a[i+1]-=sub;

		}
		System.out.println(count);
	} main {

		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] a = new int[n + 1];
		int[] b = new int[n];
		long count = 0;
		for (int i = 0; i < n + 1; i++) {
			a[i]=sc.nextInt();
		}
		for (int i = 0; i < n; i++) {
			b[i]=sc.nextInt();
		}
		for (int i = 0; i < n; i++) {
			int sub = Math.min(a[i],b[i]);
			b[i]-=sub;
			count += sub;
			sub = Math.min(a[i+1], b[i]);
			count += sub;
			a[i+1]-=sub;

		}
		System.out.println(count);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int[] a = new int[n + 1]; a new int[n + 1] n + 1 n 1 int[] b = new int[n]; b new int[n] n long count = 0; count 0 for (int i = 0; i < n + 1; i++) {
			a[i]=sc.nextInt();
		} int i = 0; int i = 0; i 0 i < n + 1 i n + 1 n 1 i++ i++ i {
			a[i]=sc.nextInt();
		} {
			a[i]=sc.nextInt();
		} a[i]=sc.nextInt() a[i] a i sc.nextInt() sc.nextInt sc for (int i = 0; i < n; i++) {
			b[i]=sc.nextInt();
		} int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
			b[i]=sc.nextInt();
		} {
			b[i]=sc.nextInt();
		} b[i]=sc.nextInt() b[i] b i sc.nextInt() sc.nextInt sc for (int i = 0; i < n; i++) {
			int sub = Math.min(a[i],b[i]);
			b[i]-=sub;
			count += sub;
			sub = Math.min(a[i+1], b[i]);
			count += sub;
			a[i+1]-=sub;

		} int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
			int sub = Math.min(a[i],b[i]);
			b[i]-=sub;
			count += sub;
			sub = Math.min(a[i+1], b[i]);
			count += sub;
			a[i+1]-=sub;

		} {
			int sub = Math.min(a[i],b[i]);
			b[i]-=sub;
			count += sub;
			sub = Math.min(a[i+1], b[i]);
			count += sub;
			a[i+1]-=sub;

		} int sub = Math.min(a[i],b[i]); sub Math.min(a[i],b[i]) Math.min Math a[i] a i b[i] b i b[i]-=sub b[i] b i sub count += sub count sub sub = Math.min(a[i+1], b[i]) sub Math.min(a[i+1], b[i]) Math.min Math a[i+1] a i+1 i 1 b[i] b i count += sub count sub a[i+1]-=sub a[i+1] a i+1 i 1 sub System.out.println(count) System.out.println System.out System System.out count String[] args args public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] a = new int[n + 1];
		int[] b = new int[n];
		long count = 0;
		for (int i = 0; i < n + 1; i++) {
			a[i]=sc.nextInt();
		}
		for (int i = 0; i < n; i++) {
			b[i]=sc.nextInt();
		}
		for (int i = 0; i < n; i++) {
			int sub = Math.min(a[i],b[i]);
			b[i]-=sub;
			count += sub;
			sub = Math.min(a[i+1], b[i]);
			count += sub;
			a[i+1]-=sub;

		}
		System.out.println(count);
	}
} public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] a = new int[n + 1];
		int[] b = new int[n];
		long count = 0;
		for (int i = 0; i < n + 1; i++) {
			a[i]=sc.nextInt();
		}
		for (int i = 0; i < n; i++) {
			b[i]=sc.nextInt();
		}
		for (int i = 0; i < n; i++) {
			int sub = Math.min(a[i],b[i]);
			b[i]-=sub;
			count += sub;
			sub = Math.min(a[i+1], b[i]);
			count += sub;
			a[i+1]-=sub;

		}
		System.out.println(count);
	}
} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] a = new int[n + 1];
		int[] b = new int[n];
		long count = 0;
		for (int i = 0; i < n + 1; i++) {
			a[i]=sc.nextInt();
		}
		for (int i = 0; i < n; i++) {
			b[i]=sc.nextInt();
		}
		for (int i = 0; i < n; i++) {
			int sub = Math.min(a[i],b[i]);
			b[i]-=sub;
			count += sub;
			sub = Math.min(a[i+1], b[i]);
			count += sub;
			a[i+1]-=sub;

		}
		System.out.println(count);
	}
}
