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();
        int[] AC = A.clone();
        long cnt = 0;

        for (int i = 0; i < N; i++) {
            if (A[i] >= B[i]) {
                A[i] -= B[i];
                B[i] = 0;
            } else {
                B[i] -= A[i];
                A[i] = 0;
            }

            if (A[i + 1] >= B[i]) {
                A[i + 1] -= B[i];
                B[i] = 0;
            } else {
                B[i] -= A[i + 1];
                A[i + 1] = 0;
            }
        }

        for (int i = 0; i < N + 1; i++) {
            cnt += AC[i] - A[i];
        }

        System.out.println(cnt);
    }
} 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();
        int[] AC = A.clone();
        long cnt = 0;

        for (int i = 0; i < N; i++) {
            if (A[i] >= B[i]) {
                A[i] -= B[i];
                B[i] = 0;
            } else {
                B[i] -= A[i];
                A[i] = 0;
            }

            if (A[i + 1] >= B[i]) {
                A[i + 1] -= B[i];
                B[i] = 0;
            } else {
                B[i] -= A[i + 1];
                A[i + 1] = 0;
            }
        }

        for (int i = 0; i < N + 1; i++) {
            cnt += AC[i] - A[i];
        }

        System.out.println(cnt);
    }
} 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();
        int[] AC = A.clone();
        long cnt = 0;

        for (int i = 0; i < N; i++) {
            if (A[i] >= B[i]) {
                A[i] -= B[i];
                B[i] = 0;
            } else {
                B[i] -= A[i];
                A[i] = 0;
            }

            if (A[i + 1] >= B[i]) {
                A[i + 1] -= B[i];
                B[i] = 0;
            } else {
                B[i] -= A[i + 1];
                A[i + 1] = 0;
            }
        }

        for (int i = 0; i < N + 1; i++) {
            cnt += AC[i] - A[i];
        }

        System.out.println(cnt);
    } 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();
        int[] AC = A.clone();
        long cnt = 0;

        for (int i = 0; i < N; i++) {
            if (A[i] >= B[i]) {
                A[i] -= B[i];
                B[i] = 0;
            } else {
                B[i] -= A[i];
                A[i] = 0;
            }

            if (A[i + 1] >= B[i]) {
                A[i + 1] -= B[i];
                B[i] = 0;
            } else {
                B[i] -= A[i + 1];
                A[i + 1] = 0;
            }
        }

        for (int i = 0; i < N + 1; i++) {
            cnt += AC[i] - A[i];
        }

        System.out.println(cnt);
    } 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] 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] B i sc.nextInt() sc.nextInt sc int[] AC = A.clone(); AC A.clone() A.clone A long cnt = 0; cnt 0 for (int i = 0; i < N; i++) {
            if (A[i] >= B[i]) {
                A[i] -= B[i];
                B[i] = 0;
            } else {
                B[i] -= A[i];
                A[i] = 0;
            }

            if (A[i + 1] >= B[i]) {
                A[i + 1] -= B[i];
                B[i] = 0;
            } else {
                B[i] -= A[i + 1];
                A[i + 1] = 0;
            }
        } int i = 0; int i = 0; i 0 i < N i N i++ i++ i {
            if (A[i] >= B[i]) {
                A[i] -= B[i];
                B[i] = 0;
            } else {
                B[i] -= A[i];
                A[i] = 0;
            }

            if (A[i + 1] >= B[i]) {
                A[i + 1] -= B[i];
                B[i] = 0;
            } else {
                B[i] -= A[i + 1];
                A[i + 1] = 0;
            }
        } {
            if (A[i] >= B[i]) {
                A[i] -= B[i];
                B[i] = 0;
            } else {
                B[i] -= A[i];
                A[i] = 0;
            }

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

        for (int i = 0; i < N; i++) {
            if (A[i] >= B[i]) {
                A[i] -= B[i];
                B[i] = 0;
            } else {
                B[i] -= A[i];
                A[i] = 0;
            }

            if (A[i + 1] >= B[i]) {
                A[i + 1] -= B[i];
                B[i] = 0;
            } else {
                B[i] -= A[i + 1];
                A[i + 1] = 0;
            }
        }

        for (int i = 0; i < N + 1; i++) {
            cnt += AC[i] - A[i];
        }

        System.out.println(cnt);
    }
} 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();
        int[] AC = A.clone();
        long cnt = 0;

        for (int i = 0; i < N; i++) {
            if (A[i] >= B[i]) {
                A[i] -= B[i];
                B[i] = 0;
            } else {
                B[i] -= A[i];
                A[i] = 0;
            }

            if (A[i + 1] >= B[i]) {
                A[i + 1] -= B[i];
                B[i] = 0;
            } else {
                B[i] -= A[i + 1];
                A[i + 1] = 0;
            }
        }

        for (int i = 0; i < N + 1; i++) {
            cnt += AC[i] - A[i];
        }

        System.out.println(cnt);
    }
} 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();
        int[] AC = A.clone();
        long cnt = 0;

        for (int i = 0; i < N; i++) {
            if (A[i] >= B[i]) {
                A[i] -= B[i];
                B[i] = 0;
            } else {
                B[i] -= A[i];
                A[i] = 0;
            }

            if (A[i + 1] >= B[i]) {
                A[i + 1] -= B[i];
                B[i] = 0;
            } else {
                B[i] -= A[i + 1];
                A[i + 1] = 0;
            }
        }

        for (int i = 0; i < N + 1; i++) {
            cnt += AC[i] - A[i];
        }

        System.out.println(cnt);
    }
}
