import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt(); long count = 0;
		int[] a = new int[n+1]; int[] b = new int[n];

		for(int i = 0; i < n+1; i++) {
			a[i] = Integer.parseInt(sc.next());
		}

		for(int i = 0; i < n; i++) {
			b[i] = Integer.parseInt(sc.next());
		}

		for(int i = 0; i < n; i++) {
			if(a[i] >= b[i]) {
				count += b[i];
			}else {
				b[i] -= a[i];
				count += a[i];
				if(a[i+1] > b[i]) {
					a[i+1] -= b[i];
					count += b[i];
				}else {
					count += a[i+1];
					a[i+1] = 0;
				}

			}
		}
		System.out.println(count);

		sc.close();
	}

} 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 count = 0;
		int[] a = new int[n+1]; int[] b = new int[n];

		for(int i = 0; i < n+1; i++) {
			a[i] = Integer.parseInt(sc.next());
		}

		for(int i = 0; i < n; i++) {
			b[i] = Integer.parseInt(sc.next());
		}

		for(int i = 0; i < n; i++) {
			if(a[i] >= b[i]) {
				count += b[i];
			}else {
				b[i] -= a[i];
				count += a[i];
				if(a[i+1] > b[i]) {
					a[i+1] -= b[i];
					count += b[i];
				}else {
					count += a[i+1];
					a[i+1] = 0;
				}

			}
		}
		System.out.println(count);

		sc.close();
	}

} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt(); long count = 0;
		int[] a = new int[n+1]; int[] b = new int[n];

		for(int i = 0; i < n+1; i++) {
			a[i] = Integer.parseInt(sc.next());
		}

		for(int i = 0; i < n; i++) {
			b[i] = Integer.parseInt(sc.next());
		}

		for(int i = 0; i < n; i++) {
			if(a[i] >= b[i]) {
				count += b[i];
			}else {
				b[i] -= a[i];
				count += a[i];
				if(a[i+1] > b[i]) {
					a[i+1] -= b[i];
					count += b[i];
				}else {
					count += a[i+1];
					a[i+1] = 0;
				}

			}
		}
		System.out.println(count);

		sc.close();
	} main {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt(); long count = 0;
		int[] a = new int[n+1]; int[] b = new int[n];

		for(int i = 0; i < n+1; i++) {
			a[i] = Integer.parseInt(sc.next());
		}

		for(int i = 0; i < n; i++) {
			b[i] = Integer.parseInt(sc.next());
		}

		for(int i = 0; i < n; i++) {
			if(a[i] >= b[i]) {
				count += b[i];
			}else {
				b[i] -= a[i];
				count += a[i];
				if(a[i+1] > b[i]) {
					a[i+1] -= b[i];
					count += b[i];
				}else {
					count += a[i+1];
					a[i+1] = 0;
				}

			}
		}
		System.out.println(count);

		sc.close();
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc long count = 0; count 0 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 for(int i = 0; i < n+1; i++) {
			a[i] = Integer.parseInt(sc.next());
		} int i = 0; int i = 0; i 0 i < n+1 i n+1 n 1 i++ i++ i {
			a[i] = Integer.parseInt(sc.next());
		} {
			a[i] = Integer.parseInt(sc.next());
		} a[i] = Integer.parseInt(sc.next()) a[i] a i Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc for(int i = 0; i < n; i++) {
			b[i] = Integer.parseInt(sc.next());
		} int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
			b[i] = Integer.parseInt(sc.next());
		} {
			b[i] = Integer.parseInt(sc.next());
		} b[i] = Integer.parseInt(sc.next()) b[i] b i Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc for(int i = 0; i < n; i++) {
			if(a[i] >= b[i]) {
				count += b[i];
			}else {
				b[i] -= a[i];
				count += a[i];
				if(a[i+1] > b[i]) {
					a[i+1] -= b[i];
					count += b[i];
				}else {
					count += a[i+1];
					a[i+1] = 0;
				}

			}
		} int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
			if(a[i] >= b[i]) {
				count += b[i];
			}else {
				b[i] -= a[i];
				count += a[i];
				if(a[i+1] > b[i]) {
					a[i+1] -= b[i];
					count += b[i];
				}else {
					count += a[i+1];
					a[i+1] = 0;
				}

			}
		} {
			if(a[i] >= b[i]) {
				count += b[i];
			}else {
				b[i] -= a[i];
				count += a[i];
				if(a[i+1] > b[i]) {
					a[i+1] -= b[i];
					count += b[i];
				}else {
					count += a[i+1];
					a[i+1] = 0;
				}

			}
		} if(a[i] >= b[i]) {
				count += b[i];
			}else {
				b[i] -= a[i];
				count += a[i];
				if(a[i+1] > b[i]) {
					a[i+1] -= b[i];
					count += b[i];
				}else {
					count += a[i+1];
					a[i+1] = 0;
				}

			} a[i] >= b[i] a[i] a i b[i] b i {
				count += b[i];
			} count += b[i] count b[i] b i {
				b[i] -= a[i];
				count += a[i];
				if(a[i+1] > b[i]) {
					a[i+1] -= b[i];
					count += b[i];
				}else {
					count += a[i+1];
					a[i+1] = 0;
				}

			} b[i] -= a[i] b[i] b i a[i] a i count += a[i] count a[i] a i if(a[i+1] > b[i]) {
					a[i+1] -= b[i];
					count += b[i];
				}else {
					count += a[i+1];
					a[i+1] = 0;
				} a[i+1] > b[i] a[i+1] a i+1 i 1 b[i] b i {
					a[i+1] -= b[i];
					count += b[i];
				} a[i+1] -= b[i] a[i+1] a i+1 i 1 b[i] b i count += b[i] count b[i] b i {
					count += a[i+1];
					a[i+1] = 0;
				} count += a[i+1] count a[i+1] a i+1 i 1 a[i+1] = 0 a[i+1] a i+1 i 1 0 System.out.println(count) System.out.println System.out System System.out count sc.close() sc.close sc String[] args args public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt(); long count = 0;
		int[] a = new int[n+1]; int[] b = new int[n];

		for(int i = 0; i < n+1; i++) {
			a[i] = Integer.parseInt(sc.next());
		}

		for(int i = 0; i < n; i++) {
			b[i] = Integer.parseInt(sc.next());
		}

		for(int i = 0; i < n; i++) {
			if(a[i] >= b[i]) {
				count += b[i];
			}else {
				b[i] -= a[i];
				count += a[i];
				if(a[i+1] > b[i]) {
					a[i+1] -= b[i];
					count += b[i];
				}else {
					count += a[i+1];
					a[i+1] = 0;
				}

			}
		}
		System.out.println(count);

		sc.close();
	}

} public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt(); long count = 0;
		int[] a = new int[n+1]; int[] b = new int[n];

		for(int i = 0; i < n+1; i++) {
			a[i] = Integer.parseInt(sc.next());
		}

		for(int i = 0; i < n; i++) {
			b[i] = Integer.parseInt(sc.next());
		}

		for(int i = 0; i < n; i++) {
			if(a[i] >= b[i]) {
				count += b[i];
			}else {
				b[i] -= a[i];
				count += a[i];
				if(a[i+1] > b[i]) {
					a[i+1] -= b[i];
					count += b[i];
				}else {
					count += a[i+1];
					a[i+1] = 0;
				}

			}
		}
		System.out.println(count);

		sc.close();
	}

} 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 count = 0;
		int[] a = new int[n+1]; int[] b = new int[n];

		for(int i = 0; i < n+1; i++) {
			a[i] = Integer.parseInt(sc.next());
		}

		for(int i = 0; i < n; i++) {
			b[i] = Integer.parseInt(sc.next());
		}

		for(int i = 0; i < n; i++) {
			if(a[i] >= b[i]) {
				count += b[i];
			}else {
				b[i] -= a[i];
				count += a[i];
				if(a[i+1] > b[i]) {
					a[i+1] -= b[i];
					count += b[i];
				}else {
					count += a[i+1];
					a[i+1] = 0;
				}

			}
		}
		System.out.println(count);

		sc.close();
	}

}