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