import java.util.*;
import java.lang.*;

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

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