import java.util.Scanner;

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