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];
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextInt();
        }

        int[] b = new int[n];
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }

        long sum = 0;
        for (int i = 0; i < n; i++) {
            if (a[i] >= b[i]) {
                sum += b[i];
                b[i] = 0;
            } else {
                sum += a[i];
                b[i] -= a[i];
            }

            if (b[i] > 0) {
                if (a[i + 1] >= b[i]) {
                    sum += b[i];
                    a[i + 1] -= b[i];
                } else {
                    sum += a[i + 1];
                    a[i + 1] = 0;
                }
            }
        }
        System.out.print(sum);
    }
} 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];
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextInt();
        }

        int[] b = new int[n];
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }

        long sum = 0;
        for (int i = 0; i < n; i++) {
            if (a[i] >= b[i]) {
                sum += b[i];
                b[i] = 0;
            } else {
                sum += a[i];
                b[i] -= a[i];
            }

            if (b[i] > 0) {
                if (a[i + 1] >= b[i]) {
                    sum += b[i];
                    a[i + 1] -= b[i];
                } else {
                    sum += a[i + 1];
                    a[i + 1] = 0;
                }
            }
        }
        System.out.print(sum);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();

        int[] a = new int[n + 1];
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextInt();
        }

        int[] b = new int[n];
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }

        long sum = 0;
        for (int i = 0; i < n; i++) {
            if (a[i] >= b[i]) {
                sum += b[i];
                b[i] = 0;
            } else {
                sum += a[i];
                b[i] -= a[i];
            }

            if (b[i] > 0) {
                if (a[i + 1] >= b[i]) {
                    sum += b[i];
                    a[i + 1] -= b[i];
                } else {
                    sum += a[i + 1];
                    a[i + 1] = 0;
                }
            }
        }
        System.out.print(sum);
    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();

        int[] a = new int[n + 1];
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextInt();
        }

        int[] b = new int[n];
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }

        long sum = 0;
        for (int i = 0; i < n; i++) {
            if (a[i] >= b[i]) {
                sum += b[i];
                b[i] = 0;
            } else {
                sum += a[i];
                b[i] -= a[i];
            }

            if (b[i] > 0) {
                if (a[i + 1] >= b[i]) {
                    sum += b[i];
                    a[i + 1] -= b[i];
                } else {
                    sum += a[i + 1];
                    a[i + 1] = 0;
                }
            }
        }
        System.out.print(sum);
    } 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 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 int[] b = new int[n]; b new int[n] n 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 sum = 0; sum 0 for (int i = 0; i < n; i++) {
            if (a[i] >= b[i]) {
                sum += b[i];
                b[i] = 0;
            } else {
                sum += a[i];
                b[i] -= a[i];
            }

            if (b[i] > 0) {
                if (a[i + 1] >= b[i]) {
                    sum += b[i];
                    a[i + 1] -= b[i];
                } else {
                    sum += 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]) {
                sum += b[i];
                b[i] = 0;
            } else {
                sum += a[i];
                b[i] -= a[i];
            }

            if (b[i] > 0) {
                if (a[i + 1] >= b[i]) {
                    sum += b[i];
                    a[i + 1] -= b[i];
                } else {
                    sum += a[i + 1];
                    a[i + 1] = 0;
                }
            }
        } {
            if (a[i] >= b[i]) {
                sum += b[i];
                b[i] = 0;
            } else {
                sum += a[i];
                b[i] -= a[i];
            }

            if (b[i] > 0) {
                if (a[i + 1] >= b[i]) {
                    sum += b[i];
                    a[i + 1] -= b[i];
                } else {
                    sum += a[i + 1];
                    a[i + 1] = 0;
                }
            }
        } if (a[i] >= b[i]) {
                sum += b[i];
                b[i] = 0;
            } else {
                sum += a[i];
                b[i] -= a[i];
            } a[i] >= b[i] a[i] a i b[i] b i {
                sum += b[i];
                b[i] = 0;
            } sum += b[i] sum b[i] b i b[i] = 0 b[i] b i 0 {
                sum += a[i];
                b[i] -= a[i];
            } sum += a[i] sum a[i] a i b[i] -= a[i] b[i] b i a[i] a i if (b[i] > 0) {
                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] > 0 b[i] b i 0 {
                if (a[i + 1] >= b[i]) {
                    sum += b[i];
                    a[i + 1] -= b[i];
                } else {
                    sum += a[i + 1];
                    a[i + 1] = 0;
                }
            } 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 System.out.print(sum) System.out.print 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();

        int[] a = new int[n + 1];
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextInt();
        }

        int[] b = new int[n];
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }

        long sum = 0;
        for (int i = 0; i < n; i++) {
            if (a[i] >= b[i]) {
                sum += b[i];
                b[i] = 0;
            } else {
                sum += a[i];
                b[i] -= a[i];
            }

            if (b[i] > 0) {
                if (a[i + 1] >= b[i]) {
                    sum += b[i];
                    a[i + 1] -= b[i];
                } else {
                    sum += a[i + 1];
                    a[i + 1] = 0;
                }
            }
        }
        System.out.print(sum);
    }
} 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];
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextInt();
        }

        int[] b = new int[n];
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }

        long sum = 0;
        for (int i = 0; i < n; i++) {
            if (a[i] >= b[i]) {
                sum += b[i];
                b[i] = 0;
            } else {
                sum += a[i];
                b[i] -= a[i];
            }

            if (b[i] > 0) {
                if (a[i + 1] >= b[i]) {
                    sum += b[i];
                    a[i + 1] -= b[i];
                } else {
                    sum += a[i + 1];
                    a[i + 1] = 0;
                }
            }
        }
        System.out.print(sum);
    }
} 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];
        for (int i = 0; i < n + 1; i++) {
            a[i] = sc.nextInt();
        }

        int[] b = new int[n];
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }

        long sum = 0;
        for (int i = 0; i < n; i++) {
            if (a[i] >= b[i]) {
                sum += b[i];
                b[i] = 0;
            } else {
                sum += a[i];
                b[i] -= a[i];
            }

            if (b[i] > 0) {
                if (a[i + 1] >= b[i]) {
                    sum += b[i];
                    a[i + 1] -= b[i];
                } else {
                    sum += a[i + 1];
                    a[i + 1] = 0;
                }
            }
        }
        System.out.print(sum);
    }
}