
import java.util.*;

public class Main {
	public static void main(String[] args) {
		Main main = new Main();
		main.run();
	}

	public void run() {
		Scanner sc = new Scanner(System.in);
		int n=sc.nextInt();
		int a[] = new int[n+1];
		int b[] = new int[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;
		for(int i=0; i<n; i++) {
			int left = Math.min(a[i], b[i]);
			a[i] -= left;
			b[i] -= left;
			ans += left;
			int right = Math.min(a[i+1], b[i]);
			a[i+1] -= right;
			b[i] -= right;
			ans += right;
		}
		System.out.println(ans);
		sc.close();
	}
} import java.util.*; util.* java public class Main {
	public static void main(String[] args) {
		Main main = new Main();
		main.run();
	}

	public void run() {
		Scanner sc = new Scanner(System.in);
		int n=sc.nextInt();
		int a[] = new int[n+1];
		int b[] = new int[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;
		for(int i=0; i<n; i++) {
			int left = Math.min(a[i], b[i]);
			a[i] -= left;
			b[i] -= left;
			ans += left;
			int right = Math.min(a[i+1], b[i]);
			a[i+1] -= right;
			b[i] -= right;
			ans += right;
		}
		System.out.println(ans);
		sc.close();
	}
} Main public static void main(String[] args) {
		Main main = new Main();
		main.run();
	} main {
		Main main = new Main();
		main.run();
	} Main main = new Main(); main new Main() main.run() main.run main String[] args args public void run() {
		Scanner sc = new Scanner(System.in);
		int n=sc.nextInt();
		int a[] = new int[n+1];
		int b[] = new int[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;
		for(int i=0; i<n; i++) {
			int left = Math.min(a[i], b[i]);
			a[i] -= left;
			b[i] -= left;
			ans += left;
			int right = Math.min(a[i+1], b[i]);
			a[i+1] -= right;
			b[i] -= right;
			ans += right;
		}
		System.out.println(ans);
		sc.close();
	} run {
		Scanner sc = new Scanner(System.in);
		int n=sc.nextInt();
		int a[] = new int[n+1];
		int b[] = new int[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;
		for(int i=0; i<n; i++) {
			int left = Math.min(a[i], b[i]);
			a[i] -= left;
			b[i] -= left;
			ans += left;
			int right = Math.min(a[i+1], b[i]);
			a[i+1] -= right;
			b[i] -= right;
			ans += right;
		}
		System.out.println(ans);
		sc.close();
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n=sc.nextInt(); n sc.nextInt() sc.nextInt sc 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]=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 for(int i=0; i<n; i++) {
			int left = Math.min(a[i], b[i]);
			a[i] -= left;
			b[i] -= left;
			ans += left;
			int right = Math.min(a[i+1], b[i]);
			a[i+1] -= right;
			b[i] -= right;
			ans += right;
		} int i=0; int i=0; i 0 i<n i n i++ i++ i {
			int left = Math.min(a[i], b[i]);
			a[i] -= left;
			b[i] -= left;
			ans += left;
			int right = Math.min(a[i+1], b[i]);
			a[i+1] -= right;
			b[i] -= right;
			ans += right;
		} {
			int left = Math.min(a[i], b[i]);
			a[i] -= left;
			b[i] -= left;
			ans += left;
			int right = Math.min(a[i+1], b[i]);
			a[i+1] -= right;
			b[i] -= right;
			ans += right;
		} int left = Math.min(a[i], b[i]); left Math.min(a[i], b[i]) Math.min Math a[i] a i b[i] b i a[i] -= left a[i] a i left b[i] -= left b[i] b i left ans += left ans left int right = Math.min(a[i+1], b[i]); right Math.min(a[i+1], b[i]) Math.min Math a[i+1] a i+1 i 1 b[i] b i a[i+1] -= right a[i+1] a i+1 i 1 right b[i] -= right b[i] b i right ans += right ans right System.out.println(ans) System.out.println System.out System System.out ans sc.close() sc.close sc public class Main {
	public static void main(String[] args) {
		Main main = new Main();
		main.run();
	}

	public void run() {
		Scanner sc = new Scanner(System.in);
		int n=sc.nextInt();
		int a[] = new int[n+1];
		int b[] = new int[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;
		for(int i=0; i<n; i++) {
			int left = Math.min(a[i], b[i]);
			a[i] -= left;
			b[i] -= left;
			ans += left;
			int right = Math.min(a[i+1], b[i]);
			a[i+1] -= right;
			b[i] -= right;
			ans += right;
		}
		System.out.println(ans);
		sc.close();
	}
} public class Main {
	public static void main(String[] args) {
		Main main = new Main();
		main.run();
	}

	public void run() {
		Scanner sc = new Scanner(System.in);
		int n=sc.nextInt();
		int a[] = new int[n+1];
		int b[] = new int[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;
		for(int i=0; i<n; i++) {
			int left = Math.min(a[i], b[i]);
			a[i] -= left;
			b[i] -= left;
			ans += left;
			int right = Math.min(a[i+1], b[i]);
			a[i+1] -= right;
			b[i] -= right;
			ans += right;
		}
		System.out.println(ans);
		sc.close();
	}
} Main

import java.util.*;

public class Main {
	public static void main(String[] args) {
		Main main = new Main();
		main.run();
	}

	public void run() {
		Scanner sc = new Scanner(System.in);
		int n=sc.nextInt();
		int a[] = new int[n+1];
		int b[] = new int[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;
		for(int i=0; i<n; i++) {
			int left = Math.min(a[i], b[i]);
			a[i] -= left;
			b[i] -= left;
			ans += left;
			int right = Math.min(a[i+1], b[i]);
			a[i+1] -= right;
			b[i] -= right;
			ans += right;
		}
		System.out.println(ans);
		sc.close();
	}
}
