import java.util.*;
public 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+1;i++){
      a[i]=sc.nextInt();
    }
    for(int i=0;i<n;i++){
      b[i]=sc.nextInt();
    }
    long answer =0;
    
    for(int i=0;i<n;i++){
      answer=answer+Math.min(a[i],b[i]);
      b[i]=Math.max(b[i]-a[i],0);
      if(b[i]>0){
        answer=answer+Math.min(a[i+1],b[i]);
        a[i+1]=Math.max(a[i+1]-b[i],0);
      }
      
      
      
    }
    System.out.println(answer);
    
    
    
  }
  

  
} import java.util.*; util.* java public 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+1;i++){
      a[i]=sc.nextInt();
    }
    for(int i=0;i<n;i++){
      b[i]=sc.nextInt();
    }
    long answer =0;
    
    for(int i=0;i<n;i++){
      answer=answer+Math.min(a[i],b[i]);
      b[i]=Math.max(b[i]-a[i],0);
      if(b[i]>0){
        answer=answer+Math.min(a[i+1],b[i]);
        a[i+1]=Math.max(a[i+1]-b[i],0);
      }
      
      
      
    }
    System.out.println(answer);
    
    
    
  }
  

  
} 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+1;i++){
      a[i]=sc.nextInt();
    }
    for(int i=0;i<n;i++){
      b[i]=sc.nextInt();
    }
    long answer =0;
    
    for(int i=0;i<n;i++){
      answer=answer+Math.min(a[i],b[i]);
      b[i]=Math.max(b[i]-a[i],0);
      if(b[i]>0){
        answer=answer+Math.min(a[i+1],b[i]);
        a[i+1]=Math.max(a[i+1]-b[i],0);
      }
      
      
      
    }
    System.out.println(answer);
    
    
    
  } 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+1;i++){
      a[i]=sc.nextInt();
    }
    for(int i=0;i<n;i++){
      b[i]=sc.nextInt();
    }
    long answer =0;
    
    for(int i=0;i<n;i++){
      answer=answer+Math.min(a[i],b[i]);
      b[i]=Math.max(b[i]-a[i],0);
      if(b[i]>0){
        answer=answer+Math.min(a[i+1],b[i]);
        a[i+1]=Math.max(a[i+1]-b[i],0);
      }
      
      
      
    }
    System.out.println(answer);
    
    
    
  } 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 answer =0; answer 0 for(int i=0;i<n;i++){
      answer=answer+Math.min(a[i],b[i]);
      b[i]=Math.max(b[i]-a[i],0);
      if(b[i]>0){
        answer=answer+Math.min(a[i+1],b[i]);
        a[i+1]=Math.max(a[i+1]-b[i],0);
      }
      
      
      
    } int i=0; int i=0; i 0 i<n i n i++ i++ i {
      answer=answer+Math.min(a[i],b[i]);
      b[i]=Math.max(b[i]-a[i],0);
      if(b[i]>0){
        answer=answer+Math.min(a[i+1],b[i]);
        a[i+1]=Math.max(a[i+1]-b[i],0);
      }
      
      
      
    } {
      answer=answer+Math.min(a[i],b[i]);
      b[i]=Math.max(b[i]-a[i],0);
      if(b[i]>0){
        answer=answer+Math.min(a[i+1],b[i]);
        a[i+1]=Math.max(a[i+1]-b[i],0);
      }
      
      
      
    } answer=answer+Math.min(a[i],b[i]) answer answer+Math.min(a[i],b[i]) answer Math.min(a[i],b[i]) Math.min Math a[i] a i b[i] b i b[i]=Math.max(b[i]-a[i],0) b[i] b i Math.max(b[i]-a[i],0) Math.max Math b[i]-a[i] b[i] b i a[i] a i 0 if(b[i]>0){
        answer=answer+Math.min(a[i+1],b[i]);
        a[i+1]=Math.max(a[i+1]-b[i],0);
      } b[i]>0 b[i] b i 0 {
        answer=answer+Math.min(a[i+1],b[i]);
        a[i+1]=Math.max(a[i+1]-b[i],0);
      } answer=answer+Math.min(a[i+1],b[i]) answer answer+Math.min(a[i+1],b[i]) answer 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]=Math.max(a[i+1]-b[i],0) a[i+1] a i+1 i 1 Math.max(a[i+1]-b[i],0) Math.max Math a[i+1]-b[i] a[i+1] a i+1 i 1 b[i] b i 0 System.out.println(answer) System.out.println System.out System System.out answer String[] args args public 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+1;i++){
      a[i]=sc.nextInt();
    }
    for(int i=0;i<n;i++){
      b[i]=sc.nextInt();
    }
    long answer =0;
    
    for(int i=0;i<n;i++){
      answer=answer+Math.min(a[i],b[i]);
      b[i]=Math.max(b[i]-a[i],0);
      if(b[i]>0){
        answer=answer+Math.min(a[i+1],b[i]);
        a[i+1]=Math.max(a[i+1]-b[i],0);
      }
      
      
      
    }
    System.out.println(answer);
    
    
    
  }
  

  
} public 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+1;i++){
      a[i]=sc.nextInt();
    }
    for(int i=0;i<n;i++){
      b[i]=sc.nextInt();
    }
    long answer =0;
    
    for(int i=0;i<n;i++){
      answer=answer+Math.min(a[i],b[i]);
      b[i]=Math.max(b[i]-a[i],0);
      if(b[i]>0){
        answer=answer+Math.min(a[i+1],b[i]);
        a[i+1]=Math.max(a[i+1]-b[i],0);
      }
      
      
      
    }
    System.out.println(answer);
    
    
    
  }
  

  
} Main
import java.util.*;
public 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+1;i++){
      a[i]=sc.nextInt();
    }
    for(int i=0;i<n;i++){
      b[i]=sc.nextInt();
    }
    long answer =0;
    
    for(int i=0;i<n;i++){
      answer=answer+Math.min(a[i],b[i]);
      b[i]=Math.max(b[i]-a[i],0);
      if(b[i]>0){
        answer=answer+Math.min(a[i+1],b[i]);
        a[i+1]=Math.max(a[i+1]-b[i],0);
      }
      
      
      
    }
    System.out.println(answer);
    
    
    
  }
  

  
}