import java.util.Scanner;

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();
        }

        long killCount = 0;

        for(int i = 0; i < n; i++){
            if(a[i] < b[i]){
                int cost = a[i];
                killCount += cost;
                a[i] -= cost;
                b[i] -= cost;

                if(a[i+1] < b[i]){
                    int costp = a[i+1];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                } else {
                    int costp = b[i];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                }
            } else {
                int cost = b[i];
                killCount += cost;
                a[i] -= cost;
                b[i] -= cost;
            }
        }
        System.out.println(killCount);
    }
} 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();
        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();
        }

        long killCount = 0;

        for(int i = 0; i < n; i++){
            if(a[i] < b[i]){
                int cost = a[i];
                killCount += cost;
                a[i] -= cost;
                b[i] -= cost;

                if(a[i+1] < b[i]){
                    int costp = a[i+1];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                } else {
                    int costp = b[i];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                }
            } else {
                int cost = b[i];
                killCount += cost;
                a[i] -= cost;
                b[i] -= cost;
            }
        }
        System.out.println(killCount);
    }
} 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();
        }

        long killCount = 0;

        for(int i = 0; i < n; i++){
            if(a[i] < b[i]){
                int cost = a[i];
                killCount += cost;
                a[i] -= cost;
                b[i] -= cost;

                if(a[i+1] < b[i]){
                    int costp = a[i+1];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                } else {
                    int costp = b[i];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                }
            } else {
                int cost = b[i];
                killCount += cost;
                a[i] -= cost;
                b[i] -= cost;
            }
        }
        System.out.println(killCount);
    } 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();
        }

        long killCount = 0;

        for(int i = 0; i < n; i++){
            if(a[i] < b[i]){
                int cost = a[i];
                killCount += cost;
                a[i] -= cost;
                b[i] -= cost;

                if(a[i+1] < b[i]){
                    int costp = a[i+1];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                } else {
                    int costp = b[i];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                }
            } else {
                int cost = b[i];
                killCount += cost;
                a[i] -= cost;
                b[i] -= cost;
            }
        }
        System.out.println(killCount);
    } 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] = 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] = sc.nextInt() b[i] b i sc.nextInt() sc.nextInt sc long killCount = 0; killCount 0 for(int i = 0; i < n; i++){
            if(a[i] < b[i]){
                int cost = a[i];
                killCount += cost;
                a[i] -= cost;
                b[i] -= cost;

                if(a[i+1] < b[i]){
                    int costp = a[i+1];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                } else {
                    int costp = b[i];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                }
            } else {
                int cost = b[i];
                killCount += cost;
                a[i] -= cost;
                b[i] -= cost;
            }
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            if(a[i] < b[i]){
                int cost = a[i];
                killCount += cost;
                a[i] -= cost;
                b[i] -= cost;

                if(a[i+1] < b[i]){
                    int costp = a[i+1];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                } else {
                    int costp = b[i];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                }
            } else {
                int cost = b[i];
                killCount += cost;
                a[i] -= cost;
                b[i] -= cost;
            }
        } {
            if(a[i] < b[i]){
                int cost = a[i];
                killCount += cost;
                a[i] -= cost;
                b[i] -= cost;

                if(a[i+1] < b[i]){
                    int costp = a[i+1];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                } else {
                    int costp = b[i];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                }
            } else {
                int cost = b[i];
                killCount += cost;
                a[i] -= cost;
                b[i] -= cost;
            }
        } if(a[i] < b[i]){
                int cost = a[i];
                killCount += cost;
                a[i] -= cost;
                b[i] -= cost;

                if(a[i+1] < b[i]){
                    int costp = a[i+1];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                } else {
                    int costp = b[i];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                }
            } else {
                int cost = b[i];
                killCount += cost;
                a[i] -= cost;
                b[i] -= cost;
            } a[i] < b[i] a[i] a i b[i] b i {
                int cost = a[i];
                killCount += cost;
                a[i] -= cost;
                b[i] -= cost;

                if(a[i+1] < b[i]){
                    int costp = a[i+1];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                } else {
                    int costp = b[i];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                }
            } int cost = a[i]; cost a[i] a i killCount += cost killCount cost a[i] -= cost a[i] a i cost b[i] -= cost b[i] b i cost if(a[i+1] < b[i]){
                    int costp = a[i+1];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                } else {
                    int costp = b[i];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                } a[i+1] < b[i] a[i+1] a i+1 i 1 b[i] b i {
                    int costp = a[i+1];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                } int costp = a[i+1]; costp a[i+1] a i+1 i 1 killCount += costp killCount costp a[i+1] -= costp a[i+1] a i+1 i 1 costp b[i] -= costp b[i] b i costp {
                    int costp = b[i];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                } int costp = b[i]; costp b[i] b i killCount += costp killCount costp a[i+1] -= costp a[i+1] a i+1 i 1 costp b[i] -= costp b[i] b i costp {
                int cost = b[i];
                killCount += cost;
                a[i] -= cost;
                b[i] -= cost;
            } int cost = b[i]; cost b[i] b i killCount += cost killCount cost a[i] -= cost a[i] a i cost b[i] -= cost b[i] b i cost System.out.println(killCount) System.out.println System.out System System.out killCount 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();
        }

        long killCount = 0;

        for(int i = 0; i < n; i++){
            if(a[i] < b[i]){
                int cost = a[i];
                killCount += cost;
                a[i] -= cost;
                b[i] -= cost;

                if(a[i+1] < b[i]){
                    int costp = a[i+1];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                } else {
                    int costp = b[i];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                }
            } else {
                int cost = b[i];
                killCount += cost;
                a[i] -= cost;
                b[i] -= cost;
            }
        }
        System.out.println(killCount);
    }
} 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();
        }

        long killCount = 0;

        for(int i = 0; i < n; i++){
            if(a[i] < b[i]){
                int cost = a[i];
                killCount += cost;
                a[i] -= cost;
                b[i] -= cost;

                if(a[i+1] < b[i]){
                    int costp = a[i+1];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                } else {
                    int costp = b[i];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                }
            } else {
                int cost = b[i];
                killCount += cost;
                a[i] -= cost;
                b[i] -= cost;
            }
        }
        System.out.println(killCount);
    }
} Main
import java.util.Scanner;

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();
        }

        long killCount = 0;

        for(int i = 0; i < n; i++){
            if(a[i] < b[i]){
                int cost = a[i];
                killCount += cost;
                a[i] -= cost;
                b[i] -= cost;

                if(a[i+1] < b[i]){
                    int costp = a[i+1];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                } else {
                    int costp = b[i];
                    killCount += costp;
                    a[i+1] -= costp;
                    b[i] -= costp;
                }
            } else {
                int cost = b[i];
                killCount += cost;
                a[i] -= cost;
                b[i] -= cost;
            }
        }
        System.out.println(killCount);
    }
}
