import java.util.Scanner;

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 sum = 0;
		for (int i=0;i<N;i++) {
			if (A[i]<B[i]) {
				B[i]-=A[i];
				sum +=A[i];
				if (A[i+1]>B[i]) {
					sum +=B[i];
					A[i+1]-=B[i];
				} else {
					sum +=A[i+1];
					A[i+1]=0;
				}
			} else {
				sum +=B[i];
			}
		}
		System.out.println(sum);
	}
} import java.util.Scanner; Scanner 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 sum = 0;
		for (int i=0;i<N;i++) {
			if (A[i]<B[i]) {
				B[i]-=A[i];
				sum +=A[i];
				if (A[i+1]>B[i]) {
					sum +=B[i];
					A[i+1]-=B[i];
				} else {
					sum +=A[i+1];
					A[i+1]=0;
				}
			} else {
				sum +=B[i];
			}
		}
		System.out.println(sum);
	}
} 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 sum = 0;
		for (int i=0;i<N;i++) {
			if (A[i]<B[i]) {
				B[i]-=A[i];
				sum +=A[i];
				if (A[i+1]>B[i]) {
					sum +=B[i];
					A[i+1]-=B[i];
				} else {
					sum +=A[i+1];
					A[i+1]=0;
				}
			} else {
				sum +=B[i];
			}
		}
		System.out.println(sum);
	} 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 sum = 0;
		for (int i=0;i<N;i++) {
			if (A[i]<B[i]) {
				B[i]-=A[i];
				sum +=A[i];
				if (A[i+1]>B[i]) {
					sum +=B[i];
					A[i+1]-=B[i];
				} else {
					sum +=A[i+1];
					A[i+1]=0;
				}
			} else {
				sum +=B[i];
			}
		}
		System.out.println(sum);
	} 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 sum = 0; sum 0 for (int i=0;i<N;i++) {
			if (A[i]<B[i]) {
				B[i]-=A[i];
				sum +=A[i];
				if (A[i+1]>B[i]) {
					sum +=B[i];
					A[i+1]-=B[i];
				} else {
					sum +=A[i+1];
					A[i+1]=0;
				}
			} else {
				sum +=B[i];
			}
		} int i=0; int i=0; i 0 i<N i N i++ i++ i {
			if (A[i]<B[i]) {
				B[i]-=A[i];
				sum +=A[i];
				if (A[i+1]>B[i]) {
					sum +=B[i];
					A[i+1]-=B[i];
				} else {
					sum +=A[i+1];
					A[i+1]=0;
				}
			} else {
				sum +=B[i];
			}
		} {
			if (A[i]<B[i]) {
				B[i]-=A[i];
				sum +=A[i];
				if (A[i+1]>B[i]) {
					sum +=B[i];
					A[i+1]-=B[i];
				} else {
					sum +=A[i+1];
					A[i+1]=0;
				}
			} else {
				sum +=B[i];
			}
		} if (A[i]<B[i]) {
				B[i]-=A[i];
				sum +=A[i];
				if (A[i+1]>B[i]) {
					sum +=B[i];
					A[i+1]-=B[i];
				} else {
					sum +=A[i+1];
					A[i+1]=0;
				}
			} else {
				sum +=B[i];
			} A[i]<B[i] A[i] A i B[i] B i {
				B[i]-=A[i];
				sum +=A[i];
				if (A[i+1]>B[i]) {
					sum +=B[i];
					A[i+1]-=B[i];
				} else {
					sum +=A[i+1];
					A[i+1]=0;
				}
			} B[i]-=A[i] B[i] B i A[i] A i sum +=A[i] sum A[i] A i if (A[i+1]>B[i]) {
					sum +=B[i];
					A[i+1]-=B[i];
				} else {
					sum +=A[i+1];
					A[i+1]=0;
				} A[i+1]>B[i] A[i+1] A i+1 i 1 B[i] B i {
					sum +=B[i];
					A[i+1]-=B[i];
				} sum +=B[i] sum B[i] B i A[i+1]-=B[i] A[i+1] A i+1 i 1 B[i] B i {
					sum +=A[i+1];
					A[i+1]=0;
				} sum +=A[i+1] sum A[i+1] A i+1 i 1 A[i+1]=0 A[i+1] A i+1 i 1 0 {
				sum +=B[i];
			} sum +=B[i] sum B[i] B i System.out.println(sum) System.out.println System.out System System.out sum 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 sum = 0;
		for (int i=0;i<N;i++) {
			if (A[i]<B[i]) {
				B[i]-=A[i];
				sum +=A[i];
				if (A[i+1]>B[i]) {
					sum +=B[i];
					A[i+1]-=B[i];
				} else {
					sum +=A[i+1];
					A[i+1]=0;
				}
			} else {
				sum +=B[i];
			}
		}
		System.out.println(sum);
	}
} 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 sum = 0;
		for (int i=0;i<N;i++) {
			if (A[i]<B[i]) {
				B[i]-=A[i];
				sum +=A[i];
				if (A[i+1]>B[i]) {
					sum +=B[i];
					A[i+1]-=B[i];
				} else {
					sum +=A[i+1];
					A[i+1]=0;
				}
			} else {
				sum +=B[i];
			}
		}
		System.out.println(sum);
	}
} Main
import java.util.Scanner;

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