import java.util.Scanner;

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

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