import 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];
		for(int i = 0; i < N + 1; i++) {
			A[i] = sc.nextLong();
		}
		for(int i = 0; i < N; i++) {
			B[i] = sc.nextLong();
		}
		long sum = 0;
		for(int i = 0; i < N; i++) {
			if(A[i] > B[i]) {
				sum += B[i];
			}
			else {
				sum += A[i];
				long temp = A[i + 1];
				A[i + 1] -= B[i] - A[i];
				A[i + 1] = Math.max(A[i + 1], 0);
				sum += temp - A[i + 1];

			}
		}
		System.out.println(sum);
	}
} import java.util.*; util.* java 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];
		for(int i = 0; i < N + 1; i++) {
			A[i] = sc.nextLong();
		}
		for(int i = 0; i < N; i++) {
			B[i] = sc.nextLong();
		}
		long sum = 0;
		for(int i = 0; i < N; i++) {
			if(A[i] > B[i]) {
				sum += B[i];
			}
			else {
				sum += A[i];
				long temp = A[i + 1];
				A[i + 1] -= B[i] - A[i];
				A[i + 1] = Math.max(A[i + 1], 0);
				sum += temp - A[i + 1];

			}
		}
		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];
		for(int i = 0; i < N + 1; i++) {
			A[i] = sc.nextLong();
		}
		for(int i = 0; i < N; i++) {
			B[i] = sc.nextLong();
		}
		long sum = 0;
		for(int i = 0; i < N; i++) {
			if(A[i] > B[i]) {
				sum += B[i];
			}
			else {
				sum += A[i];
				long temp = A[i + 1];
				A[i + 1] -= B[i] - A[i];
				A[i + 1] = Math.max(A[i + 1], 0);
				sum += temp - A[i + 1];

			}
		}
		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];
		for(int i = 0; i < N + 1; i++) {
			A[i] = sc.nextLong();
		}
		for(int i = 0; i < N; i++) {
			B[i] = sc.nextLong();
		}
		long sum = 0;
		for(int i = 0; i < N; i++) {
			if(A[i] > B[i]) {
				sum += B[i];
			}
			else {
				sum += A[i];
				long temp = A[i + 1];
				A[i + 1] -= B[i] - A[i];
				A[i + 1] = Math.max(A[i + 1], 0);
				sum += temp - A[i + 1];

			}
		}
		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 for(int i = 0; i < N + 1; i++) {
			A[i] = sc.nextLong();
		} int i = 0; int i = 0; i 0 i < N + 1 i N + 1 N 1 i++ i++ i {
			A[i] = sc.nextLong();
		} {
			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] = sc.nextLong() B[i] B i sc.nextLong() sc.nextLong sc long sum = 0; sum 0 for(int i = 0; i < N; i++) {
			if(A[i] > B[i]) {
				sum += B[i];
			}
			else {
				sum += A[i];
				long temp = A[i + 1];
				A[i + 1] -= B[i] - A[i];
				A[i + 1] = Math.max(A[i + 1], 0);
				sum += temp - A[i + 1];

			}
		} int i = 0; int i = 0; i 0 i < N i N i++ i++ i {
			if(A[i] > B[i]) {
				sum += B[i];
			}
			else {
				sum += A[i];
				long temp = A[i + 1];
				A[i + 1] -= B[i] - A[i];
				A[i + 1] = Math.max(A[i + 1], 0);
				sum += temp - A[i + 1];

			}
		} {
			if(A[i] > B[i]) {
				sum += B[i];
			}
			else {
				sum += A[i];
				long temp = A[i + 1];
				A[i + 1] -= B[i] - A[i];
				A[i + 1] = Math.max(A[i + 1], 0);
				sum += temp - A[i + 1];

			}
		} if(A[i] > B[i]) {
				sum += B[i];
			}
			else {
				sum += A[i];
				long temp = A[i + 1];
				A[i + 1] -= B[i] - A[i];
				A[i + 1] = Math.max(A[i + 1], 0);
				sum += temp - A[i + 1];

			} A[i] > B[i] A[i] A i B[i] B i {
				sum += B[i];
			} sum += B[i] sum B[i] B i {
				sum += A[i];
				long temp = A[i + 1];
				A[i + 1] -= B[i] - A[i];
				A[i + 1] = Math.max(A[i + 1], 0);
				sum += temp - A[i + 1];

			} sum += A[i] sum A[i] A i long temp = A[i + 1]; temp A[i + 1] A i + 1 i 1 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 A[i + 1] = Math.max(A[i + 1], 0) A[i + 1] A i + 1 i 1 Math.max(A[i + 1], 0) Math.max Math A[i + 1] A i + 1 i 1 0 sum += temp - A[i + 1] sum temp - A[i + 1] temp A[i + 1] A i + 1 i 1 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];
		for(int i = 0; i < N + 1; i++) {
			A[i] = sc.nextLong();
		}
		for(int i = 0; i < N; i++) {
			B[i] = sc.nextLong();
		}
		long sum = 0;
		for(int i = 0; i < N; i++) {
			if(A[i] > B[i]) {
				sum += B[i];
			}
			else {
				sum += A[i];
				long temp = A[i + 1];
				A[i + 1] -= B[i] - A[i];
				A[i + 1] = Math.max(A[i + 1], 0);
				sum += temp - A[i + 1];

			}
		}
		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];
		for(int i = 0; i < N + 1; i++) {
			A[i] = sc.nextLong();
		}
		for(int i = 0; i < N; i++) {
			B[i] = sc.nextLong();
		}
		long sum = 0;
		for(int i = 0; i < N; i++) {
			if(A[i] > B[i]) {
				sum += B[i];
			}
			else {
				sum += A[i];
				long temp = A[i + 1];
				A[i + 1] -= B[i] - A[i];
				A[i + 1] = Math.max(A[i + 1], 0);
				sum += temp - A[i + 1];

			}
		}
		System.out.println(sum);
	}
} Main
import 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];
		for(int i = 0; i < N + 1; i++) {
			A[i] = sc.nextLong();
		}
		for(int i = 0; i < N; i++) {
			B[i] = sc.nextLong();
		}
		long sum = 0;
		for(int i = 0; i < N; i++) {
			if(A[i] > B[i]) {
				sum += B[i];
			}
			else {
				sum += A[i];
				long temp = A[i + 1];
				A[i + 1] -= B[i] - A[i];
				A[i + 1] = Math.max(A[i + 1], 0);
				sum += temp - A[i + 1];

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