import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		try (Scanner sc = new Scanner(System.in)) {

			int n = sc.nextInt();
			Integer[] a = new Integer[n + 1];
			Integer[] b = new Integer[n];
			for(int i = 0 ; i < n + 1 ; i++) {
				a[i] = sc.nextInt();
			}
			for(int i = 0 ; i < n ; i++) {
				b[i] = sc.nextInt();
			}
			long ans = 0;
			int zan = a[0];
			for(int i = 0 ; i < n ; i++) {
				if(zan < b[i]) {
					b[i] -= zan;
					ans += zan;
					if(a[i + 1] < b[i]) {
						ans += a[i + 1];
						zan = 0;
					} else {
						ans += b[i];
						zan = a[i + 1] - b[i];
					}
				} else {
					ans += b[i];
					zan = a[i + 1];
				}
			}
			System.out.println(ans);

		}
	}

} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {

		try (Scanner sc = new Scanner(System.in)) {

			int n = sc.nextInt();
			Integer[] a = new Integer[n + 1];
			Integer[] b = new Integer[n];
			for(int i = 0 ; i < n + 1 ; i++) {
				a[i] = sc.nextInt();
			}
			for(int i = 0 ; i < n ; i++) {
				b[i] = sc.nextInt();
			}
			long ans = 0;
			int zan = a[0];
			for(int i = 0 ; i < n ; i++) {
				if(zan < b[i]) {
					b[i] -= zan;
					ans += zan;
					if(a[i + 1] < b[i]) {
						ans += a[i + 1];
						zan = 0;
					} else {
						ans += b[i];
						zan = a[i + 1] - b[i];
					}
				} else {
					ans += b[i];
					zan = a[i + 1];
				}
			}
			System.out.println(ans);

		}
	}

} Main public static void main(String[] args) {

		try (Scanner sc = new Scanner(System.in)) {

			int n = sc.nextInt();
			Integer[] a = new Integer[n + 1];
			Integer[] b = new Integer[n];
			for(int i = 0 ; i < n + 1 ; i++) {
				a[i] = sc.nextInt();
			}
			for(int i = 0 ; i < n ; i++) {
				b[i] = sc.nextInt();
			}
			long ans = 0;
			int zan = a[0];
			for(int i = 0 ; i < n ; i++) {
				if(zan < b[i]) {
					b[i] -= zan;
					ans += zan;
					if(a[i + 1] < b[i]) {
						ans += a[i + 1];
						zan = 0;
					} else {
						ans += b[i];
						zan = a[i + 1] - b[i];
					}
				} else {
					ans += b[i];
					zan = a[i + 1];
				}
			}
			System.out.println(ans);

		}
	} main {

		try (Scanner sc = new Scanner(System.in)) {

			int n = sc.nextInt();
			Integer[] a = new Integer[n + 1];
			Integer[] b = new Integer[n];
			for(int i = 0 ; i < n + 1 ; i++) {
				a[i] = sc.nextInt();
			}
			for(int i = 0 ; i < n ; i++) {
				b[i] = sc.nextInt();
			}
			long ans = 0;
			int zan = a[0];
			for(int i = 0 ; i < n ; i++) {
				if(zan < b[i]) {
					b[i] -= zan;
					ans += zan;
					if(a[i + 1] < b[i]) {
						ans += a[i + 1];
						zan = 0;
					} else {
						ans += b[i];
						zan = a[i + 1] - b[i];
					}
				} else {
					ans += b[i];
					zan = a[i + 1];
				}
			}
			System.out.println(ans);

		}
	} try (Scanner sc = new Scanner(System.in)) {

			int n = sc.nextInt();
			Integer[] a = new Integer[n + 1];
			Integer[] b = new Integer[n];
			for(int i = 0 ; i < n + 1 ; i++) {
				a[i] = sc.nextInt();
			}
			for(int i = 0 ; i < n ; i++) {
				b[i] = sc.nextInt();
			}
			long ans = 0;
			int zan = a[0];
			for(int i = 0 ; i < n ; i++) {
				if(zan < b[i]) {
					b[i] -= zan;
					ans += zan;
					if(a[i + 1] < b[i]) {
						ans += a[i + 1];
						zan = 0;
					} else {
						ans += b[i];
						zan = a[i + 1] - b[i];
					}
				} else {
					ans += b[i];
					zan = a[i + 1];
				}
			}
			System.out.println(ans);

		} {

			int n = sc.nextInt();
			Integer[] a = new Integer[n + 1];
			Integer[] b = new Integer[n];
			for(int i = 0 ; i < n + 1 ; i++) {
				a[i] = sc.nextInt();
			}
			for(int i = 0 ; i < n ; i++) {
				b[i] = sc.nextInt();
			}
			long ans = 0;
			int zan = a[0];
			for(int i = 0 ; i < n ; i++) {
				if(zan < b[i]) {
					b[i] -= zan;
					ans += zan;
					if(a[i + 1] < b[i]) {
						ans += a[i + 1];
						zan = 0;
					} else {
						ans += b[i];
						zan = a[i + 1] - b[i];
					}
				} else {
					ans += b[i];
					zan = a[i + 1];
				}
			}
			System.out.println(ans);

		} Scanner sc = new Scanner(System.in) Scanner sc = new Scanner(System.in) new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc Integer[] a = new Integer[n + 1]; a new Integer[n + 1] n + 1 n 1 Integer[] b = new Integer[n]; b new Integer[n] n 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 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 ans = 0; ans 0 int zan = a[0]; zan a[0] a 0 for(int i = 0 ; i < n ; i++) {
				if(zan < b[i]) {
					b[i] -= zan;
					ans += zan;
					if(a[i + 1] < b[i]) {
						ans += a[i + 1];
						zan = 0;
					} else {
						ans += b[i];
						zan = a[i + 1] - b[i];
					}
				} else {
					ans += b[i];
					zan = a[i + 1];
				}
			} int i = 0 ; int i = 0 ; i 0 i < n i n i++ i++ i {
				if(zan < b[i]) {
					b[i] -= zan;
					ans += zan;
					if(a[i + 1] < b[i]) {
						ans += a[i + 1];
						zan = 0;
					} else {
						ans += b[i];
						zan = a[i + 1] - b[i];
					}
				} else {
					ans += b[i];
					zan = a[i + 1];
				}
			} {
				if(zan < b[i]) {
					b[i] -= zan;
					ans += zan;
					if(a[i + 1] < b[i]) {
						ans += a[i + 1];
						zan = 0;
					} else {
						ans += b[i];
						zan = a[i + 1] - b[i];
					}
				} else {
					ans += b[i];
					zan = a[i + 1];
				}
			} if(zan < b[i]) {
					b[i] -= zan;
					ans += zan;
					if(a[i + 1] < b[i]) {
						ans += a[i + 1];
						zan = 0;
					} else {
						ans += b[i];
						zan = a[i + 1] - b[i];
					}
				} else {
					ans += b[i];
					zan = a[i + 1];
				} zan < b[i] zan b[i] b i {
					b[i] -= zan;
					ans += zan;
					if(a[i + 1] < b[i]) {
						ans += a[i + 1];
						zan = 0;
					} else {
						ans += b[i];
						zan = a[i + 1] - b[i];
					}
				} b[i] -= zan b[i] b i zan ans += zan ans zan if(a[i + 1] < b[i]) {
						ans += a[i + 1];
						zan = 0;
					} else {
						ans += b[i];
						zan = a[i + 1] - b[i];
					} a[i + 1] < b[i] a[i + 1] a i + 1 i 1 b[i] b i {
						ans += a[i + 1];
						zan = 0;
					} ans += a[i + 1] ans a[i + 1] a i + 1 i 1 zan = 0 zan 0 {
						ans += b[i];
						zan = a[i + 1] - b[i];
					} ans += b[i] ans b[i] b i zan = a[i + 1] - b[i] zan a[i + 1] - b[i] a[i + 1] a i + 1 i 1 b[i] b i {
					ans += b[i];
					zan = a[i + 1];
				} ans += b[i] ans b[i] b i zan = a[i + 1] zan a[i + 1] a i + 1 i 1 System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {

	public static void main(String[] args) {

		try (Scanner sc = new Scanner(System.in)) {

			int n = sc.nextInt();
			Integer[] a = new Integer[n + 1];
			Integer[] b = new Integer[n];
			for(int i = 0 ; i < n + 1 ; i++) {
				a[i] = sc.nextInt();
			}
			for(int i = 0 ; i < n ; i++) {
				b[i] = sc.nextInt();
			}
			long ans = 0;
			int zan = a[0];
			for(int i = 0 ; i < n ; i++) {
				if(zan < b[i]) {
					b[i] -= zan;
					ans += zan;
					if(a[i + 1] < b[i]) {
						ans += a[i + 1];
						zan = 0;
					} else {
						ans += b[i];
						zan = a[i + 1] - b[i];
					}
				} else {
					ans += b[i];
					zan = a[i + 1];
				}
			}
			System.out.println(ans);

		}
	}

} public class Main {

	public static void main(String[] args) {

		try (Scanner sc = new Scanner(System.in)) {

			int n = sc.nextInt();
			Integer[] a = new Integer[n + 1];
			Integer[] b = new Integer[n];
			for(int i = 0 ; i < n + 1 ; i++) {
				a[i] = sc.nextInt();
			}
			for(int i = 0 ; i < n ; i++) {
				b[i] = sc.nextInt();
			}
			long ans = 0;
			int zan = a[0];
			for(int i = 0 ; i < n ; i++) {
				if(zan < b[i]) {
					b[i] -= zan;
					ans += zan;
					if(a[i + 1] < b[i]) {
						ans += a[i + 1];
						zan = 0;
					} else {
						ans += b[i];
						zan = a[i + 1] - b[i];
					}
				} else {
					ans += b[i];
					zan = a[i + 1];
				}
			}
			System.out.println(ans);

		}
	}

} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		try (Scanner sc = new Scanner(System.in)) {

			int n = sc.nextInt();
			Integer[] a = new Integer[n + 1];
			Integer[] b = new Integer[n];
			for(int i = 0 ; i < n + 1 ; i++) {
				a[i] = sc.nextInt();
			}
			for(int i = 0 ; i < n ; i++) {
				b[i] = sc.nextInt();
			}
			long ans = 0;
			int zan = a[0];
			for(int i = 0 ; i < n ; i++) {
				if(zan < b[i]) {
					b[i] -= zan;
					ans += zan;
					if(a[i + 1] < b[i]) {
						ans += a[i + 1];
						zan = 0;
					} else {
						ans += b[i];
						zan = a[i + 1] - b[i];
					}
				} else {
					ans += b[i];
					zan = a[i + 1];
				}
			}
			System.out.println(ans);

		}
	}

}
