import java.util.*;

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

class Main{
  public static void main(String args[]){
    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;i++){
      a[i]=sc.nextInt();
    }
    for(int i=0;i<n;i++){
      b[i]=sc.nextInt();
    }
    long df=0;
    for(int i=0;i<n;i++){
      int kl=Math.min(a[i],b[i]);
      df+=kl;
      b[i]=b[i]-kl;
      kl=Math.min(a[i+1],b[i]);
      df+=kl;
      a[i+1]=a[i+1]-kl;
    }
    System.out.println(df);
  }
}