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+1];
		long[] b=new long[n];
		long sum=0;

		for(int i=0;i<=n;i++) a[i]=sc.nextLong();

		for(int i=0;i<n;i++) b[i]=sc.nextLong();

		for(int i=n-1;i>=0;i--) {
			sum+=Math.min(a[i+1], b[i]);
			b[i]=Math.max(0, b[i]-a[i+1]);
			sum+=Math.min(a[i], b[i]);
			a[i]=Math.max(0, a[i]-b[i]);
		}
		System.out.println(sum);
	}
}
 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+1];
		long[] b=new long[n];
		long sum=0;

		for(int i=0;i<=n;i++) a[i]=sc.nextLong();

		for(int i=0;i<n;i++) b[i]=sc.nextLong();

		for(int i=n-1;i>=0;i--) {
			sum+=Math.min(a[i+1], b[i]);
			b[i]=Math.max(0, b[i]-a[i+1]);
			sum+=Math.min(a[i], b[i]);
			a[i]=Math.max(0, a[i]-b[i]);
		}
		System.out.println(sum);
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n=sc.nextInt();
		long[] a=new long[n+1];
		long[] b=new long[n];
		long sum=0;

		for(int i=0;i<=n;i++) a[i]=sc.nextLong();

		for(int i=0;i<n;i++) b[i]=sc.nextLong();

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

		for(int i=0;i<=n;i++) a[i]=sc.nextLong();

		for(int i=0;i<n;i++) b[i]=sc.nextLong();

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

		for(int i=0;i<=n;i++) a[i]=sc.nextLong();

		for(int i=0;i<n;i++) b[i]=sc.nextLong();

		for(int i=n-1;i>=0;i--) {
			sum+=Math.min(a[i+1], b[i]);
			b[i]=Math.max(0, b[i]-a[i+1]);
			sum+=Math.min(a[i], b[i]);
			a[i]=Math.max(0, a[i]-b[i]);
		}
		System.out.println(sum);
	}
} public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n=sc.nextInt();
		long[] a=new long[n+1];
		long[] b=new long[n];
		long sum=0;

		for(int i=0;i<=n;i++) a[i]=sc.nextLong();

		for(int i=0;i<n;i++) b[i]=sc.nextLong();

		for(int i=n-1;i>=0;i--) {
			sum+=Math.min(a[i+1], b[i]);
			b[i]=Math.max(0, b[i]-a[i+1]);
			sum+=Math.min(a[i], b[i]);
			a[i]=Math.max(0, a[i]-b[i]);
		}
		System.out.println(sum);
	}
} 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+1];
		long[] b=new long[n];
		long sum=0;

		for(int i=0;i<=n;i++) a[i]=sc.nextLong();

		for(int i=0;i<n;i++) b[i]=sc.nextLong();

		for(int i=n-1;i>=0;i--) {
			sum+=Math.min(a[i+1], b[i]);
			b[i]=Math.max(0, b[i]-a[i+1]);
			sum+=Math.min(a[i], b[i]);
			a[i]=Math.max(0, a[i]-b[i]);
		}
		System.out.println(sum);
	}
}

