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 ans = 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 c = Math.min(a[i],b[i]);ans+=c;a[i]-=c;b[i]-=c;
                            long d = Math.min(a[i+1],b[i]);ans+=d;a[i+1]-=d;b[i]-=d;
                            }
		System.out.println(ans);
	}
} 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 ans = 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 c = Math.min(a[i],b[i]);ans+=c;a[i]-=c;b[i]-=c;
                            long d = Math.min(a[i+1],b[i]);ans+=d;a[i+1]-=d;b[i]-=d;
                            }
		System.out.println(ans);
	}
} 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 ans = 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 c = Math.min(a[i],b[i]);ans+=c;a[i]-=c;b[i]-=c;
                            long d = Math.min(a[i+1],b[i]);ans+=d;a[i+1]-=d;b[i]-=d;
                            }
		System.out.println(ans);
	} main {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt(); 
        long [] a = new long [n+1];
        long [] b = new long [n];
        long ans = 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 c = Math.min(a[i],b[i]);ans+=c;a[i]-=c;b[i]-=c;
                            long d = Math.min(a[i+1],b[i]);ans+=d;a[i+1]-=d;b[i]-=d;
                            }
		System.out.println(ans);
	} 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 ans = 0; ans 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] = 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] = sc.nextLong() b[i] b i sc.nextLong() sc.nextLong sc for(int i=0;i<n;i++){long c = Math.min(a[i],b[i]);ans+=c;a[i]-=c;b[i]-=c;
                            long d = Math.min(a[i+1],b[i]);ans+=d;a[i+1]-=d;b[i]-=d;
                            } int i=0; int i=0; i 0 i<n i n i++ i++ i {long c = Math.min(a[i],b[i]);ans+=c;a[i]-=c;b[i]-=c;
                            long d = Math.min(a[i+1],b[i]);ans+=d;a[i+1]-=d;b[i]-=d;
                            } {long c = Math.min(a[i],b[i]);ans+=c;a[i]-=c;b[i]-=c;
                            long d = Math.min(a[i+1],b[i]);ans+=d;a[i+1]-=d;b[i]-=d;
                            } long c = Math.min(a[i],b[i]); c Math.min(a[i],b[i]) Math.min Math a[i] a i b[i] b i ans+=c ans c a[i]-=c a[i] a i c b[i]-=c b[i] b i c long d = Math.min(a[i+1],b[i]); d Math.min(a[i+1],b[i]) Math.min Math a[i+1] a i+1 i 1 b[i] b i ans+=d ans d a[i+1]-=d a[i+1] a i+1 i 1 d b[i]-=d b[i] b i d System.out.println(ans) System.out.println System.out System System.out ans 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 ans = 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 c = Math.min(a[i],b[i]);ans+=c;a[i]-=c;b[i]-=c;
                            long d = Math.min(a[i+1],b[i]);ans+=d;a[i+1]-=d;b[i]-=d;
                            }
		System.out.println(ans);
	}
} 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 ans = 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 c = Math.min(a[i],b[i]);ans+=c;a[i]-=c;b[i]-=c;
                            long d = Math.min(a[i+1],b[i]);ans+=d;a[i+1]-=d;b[i]-=d;
                            }
		System.out.println(ans);
	}
} 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 ans = 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 c = Math.min(a[i],b[i]);ans+=c;a[i]-=c;b[i]-=c;
                            long d = Math.min(a[i+1],b[i]);ans+=d;a[i+1]-=d;b[i]-=d;
                            }
		System.out.println(ans);
	}
}
