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];
		for( int i=0; i<N+1; i++ ){
			A[i] = sc.nextLong();
		}
		for( int i=0; i<N; i++ ){
			B[i] = sc.nextLong();
		}
		long ans = 0;
		for( int i=0; i<N; i++ ){
			if( B[i]<=A[i] ){
				ans += B[i];
			}else{
				if( B[i]<=A[i]+A[i+1] ){
					ans += B[i]; 
				}else{
					ans += A[i]+A[i+1];
				}
				A[i+1] -= B[i] - A[i];
				if( A[i+1]<0 ){
					A[i+1] = 0;
				}
			}
		}
		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];
		for( int i=0; i<N+1; i++ ){
			A[i] = sc.nextLong();
		}
		for( int i=0; i<N; i++ ){
			B[i] = sc.nextLong();
		}
		long ans = 0;
		for( int i=0; i<N; i++ ){
			if( B[i]<=A[i] ){
				ans += B[i];
			}else{
				if( B[i]<=A[i]+A[i+1] ){
					ans += B[i]; 
				}else{
					ans += A[i]+A[i+1];
				}
				A[i+1] -= B[i] - A[i];
				if( A[i+1]<0 ){
					A[i+1] = 0;
				}
			}
		}
		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];
		for( int i=0; i<N+1; i++ ){
			A[i] = sc.nextLong();
		}
		for( int i=0; i<N; i++ ){
			B[i] = sc.nextLong();
		}
		long ans = 0;
		for( int i=0; i<N; i++ ){
			if( B[i]<=A[i] ){
				ans += B[i];
			}else{
				if( B[i]<=A[i]+A[i+1] ){
					ans += B[i]; 
				}else{
					ans += A[i]+A[i+1];
				}
				A[i+1] -= B[i] - A[i];
				if( A[i+1]<0 ){
					A[i+1] = 0;
				}
			}
		}
		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];
		for( int i=0; i<N+1; i++ ){
			A[i] = sc.nextLong();
		}
		for( int i=0; i<N; i++ ){
			B[i] = sc.nextLong();
		}
		long ans = 0;
		for( int i=0; i<N; i++ ){
			if( B[i]<=A[i] ){
				ans += B[i];
			}else{
				if( B[i]<=A[i]+A[i+1] ){
					ans += B[i]; 
				}else{
					ans += A[i]+A[i+1];
				}
				A[i+1] -= B[i] - A[i];
				if( A[i+1]<0 ){
					A[i+1] = 0;
				}
			}
		}
		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 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 long ans = 0; ans 0 for( int i=0; i<N; i++ ){
			if( B[i]<=A[i] ){
				ans += B[i];
			}else{
				if( B[i]<=A[i]+A[i+1] ){
					ans += B[i]; 
				}else{
					ans += A[i]+A[i+1];
				}
				A[i+1] -= B[i] - A[i];
				if( A[i+1]<0 ){
					A[i+1] = 0;
				}
			}
		} int i=0; int i=0; i 0 i<N i N i++ i++ i {
			if( B[i]<=A[i] ){
				ans += B[i];
			}else{
				if( B[i]<=A[i]+A[i+1] ){
					ans += B[i]; 
				}else{
					ans += A[i]+A[i+1];
				}
				A[i+1] -= B[i] - A[i];
				if( A[i+1]<0 ){
					A[i+1] = 0;
				}
			}
		} {
			if( B[i]<=A[i] ){
				ans += B[i];
			}else{
				if( B[i]<=A[i]+A[i+1] ){
					ans += B[i]; 
				}else{
					ans += A[i]+A[i+1];
				}
				A[i+1] -= B[i] - A[i];
				if( A[i+1]<0 ){
					A[i+1] = 0;
				}
			}
		} if( B[i]<=A[i] ){
				ans += B[i];
			}else{
				if( B[i]<=A[i]+A[i+1] ){
					ans += B[i]; 
				}else{
					ans += A[i]+A[i+1];
				}
				A[i+1] -= B[i] - A[i];
				if( A[i+1]<0 ){
					A[i+1] = 0;
				}
			} B[i]<=A[i] B[i] B i A[i] A i {
				ans += B[i];
			} ans += B[i] ans B[i] B i {
				if( B[i]<=A[i]+A[i+1] ){
					ans += B[i]; 
				}else{
					ans += A[i]+A[i+1];
				}
				A[i+1] -= B[i] - A[i];
				if( A[i+1]<0 ){
					A[i+1] = 0;
				}
			} if( B[i]<=A[i]+A[i+1] ){
					ans += B[i]; 
				}else{
					ans += A[i]+A[i+1];
				} B[i]<=A[i]+A[i+1] B[i] B i A[i]+A[i+1] A[i] A i A[i+1] A i+1 i 1 {
					ans += B[i]; 
				} ans += B[i] ans B[i] B i {
					ans += A[i]+A[i+1];
				} ans += A[i]+A[i+1] ans A[i]+A[i+1] A[i] A i A[i+1] A i+1 i 1 A[i+1] -= B[i] - A[i] A[i+1] A i+1 i 1 B[i] - A[i] B[i] B i A[i] A i if( A[i+1]<0 ){
					A[i+1] = 0;
				} A[i+1]<0 A[i+1] A i+1 i 1 0 {
					A[i+1] = 0;
				} A[i+1] = 0 A[i+1] A i+1 i 1 0 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];
		for( int i=0; i<N+1; i++ ){
			A[i] = sc.nextLong();
		}
		for( int i=0; i<N; i++ ){
			B[i] = sc.nextLong();
		}
		long ans = 0;
		for( int i=0; i<N; i++ ){
			if( B[i]<=A[i] ){
				ans += B[i];
			}else{
				if( B[i]<=A[i]+A[i+1] ){
					ans += B[i]; 
				}else{
					ans += A[i]+A[i+1];
				}
				A[i+1] -= B[i] - A[i];
				if( A[i+1]<0 ){
					A[i+1] = 0;
				}
			}
		}
		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];
		for( int i=0; i<N+1; i++ ){
			A[i] = sc.nextLong();
		}
		for( int i=0; i<N; i++ ){
			B[i] = sc.nextLong();
		}
		long ans = 0;
		for( int i=0; i<N; i++ ){
			if( B[i]<=A[i] ){
				ans += B[i];
			}else{
				if( B[i]<=A[i]+A[i+1] ){
					ans += B[i]; 
				}else{
					ans += A[i]+A[i+1];
				}
				A[i+1] -= B[i] - A[i];
				if( A[i+1]<0 ){
					A[i+1] = 0;
				}
			}
		}
		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];
		for( int i=0; i<N+1; i++ ){
			A[i] = sc.nextLong();
		}
		for( int i=0; i<N; i++ ){
			B[i] = sc.nextLong();
		}
		long ans = 0;
		for( int i=0; i<N; i++ ){
			if( B[i]<=A[i] ){
				ans += B[i];
			}else{
				if( B[i]<=A[i]+A[i+1] ){
					ans += B[i]; 
				}else{
					ans += A[i]+A[i+1];
				}
				A[i+1] -= B[i] - A[i];
				if( A[i+1]<0 ){
					A[i+1] = 0;
				}
			}
		}
		System.out.println(ans);
	}
}
