import java.util.*;
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 monsters = 0;
        for(int i = 0; i<n; i++) {

            if(a[i]>=b[i]) {
                monsters += b[i];
                //System.out.println(monsters + " " + a[i+1]);
                continue;
            }
            //System.out.println(b[i]);
            monsters += a[i];
            b[i] = b[i]-a[i];
            //System.out.println(b[i]);
            //System.out.println("monsters" + monsters);
            monsters += Math.min(a[i+1],b[i]);
            a[i+1] = Math.max(0,a[i+1]-b[i]);
            //System.out.println(monsters + " " + a[i+1]);
        }
        System.out.println(monsters);
    }
} import java.util.*; util.* java 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 monsters = 0;
        for(int i = 0; i<n; i++) {

            if(a[i]>=b[i]) {
                monsters += b[i];
                //System.out.println(monsters + " " + a[i+1]);
                continue;
            }
            //System.out.println(b[i]);
            monsters += a[i];
            b[i] = b[i]-a[i];
            //System.out.println(b[i]);
            //System.out.println("monsters" + monsters);
            monsters += Math.min(a[i+1],b[i]);
            a[i+1] = Math.max(0,a[i+1]-b[i]);
            //System.out.println(monsters + " " + a[i+1]);
        }
        System.out.println(monsters);
    }
} 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 monsters = 0;
        for(int i = 0; i<n; i++) {

            if(a[i]>=b[i]) {
                monsters += b[i];
                //System.out.println(monsters + " " + a[i+1]);
                continue;
            }
            //System.out.println(b[i]);
            monsters += a[i];
            b[i] = b[i]-a[i];
            //System.out.println(b[i]);
            //System.out.println("monsters" + monsters);
            monsters += Math.min(a[i+1],b[i]);
            a[i+1] = Math.max(0,a[i+1]-b[i]);
            //System.out.println(monsters + " " + a[i+1]);
        }
        System.out.println(monsters);
    } 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 monsters = 0;
        for(int i = 0; i<n; i++) {

            if(a[i]>=b[i]) {
                monsters += b[i];
                //System.out.println(monsters + " " + a[i+1]);
                continue;
            }
            //System.out.println(b[i]);
            monsters += a[i];
            b[i] = b[i]-a[i];
            //System.out.println(b[i]);
            //System.out.println("monsters" + monsters);
            monsters += Math.min(a[i+1],b[i]);
            a[i+1] = Math.max(0,a[i+1]-b[i]);
            //System.out.println(monsters + " " + a[i+1]);
        }
        System.out.println(monsters);
    } 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 monsters = 0; monsters 0 for(int i = 0; i<n; i++) {

            if(a[i]>=b[i]) {
                monsters += b[i];
                //System.out.println(monsters + " " + a[i+1]);
                continue;
            }
            //System.out.println(b[i]);
            monsters += a[i];
            b[i] = b[i]-a[i];
            //System.out.println(b[i]);
            //System.out.println("monsters" + monsters);
            monsters += Math.min(a[i+1],b[i]);
            a[i+1] = Math.max(0,a[i+1]-b[i]);
            //System.out.println(monsters + " " + a[i+1]);
        } int i = 0; int i = 0; i 0 i<n i n i++ i++ i {

            if(a[i]>=b[i]) {
                monsters += b[i];
                //System.out.println(monsters + " " + a[i+1]);
                continue;
            }
            //System.out.println(b[i]);
            monsters += a[i];
            b[i] = b[i]-a[i];
            //System.out.println(b[i]);
            //System.out.println("monsters" + monsters);
            monsters += Math.min(a[i+1],b[i]);
            a[i+1] = Math.max(0,a[i+1]-b[i]);
            //System.out.println(monsters + " " + a[i+1]);
        } {

            if(a[i]>=b[i]) {
                monsters += b[i];
                //System.out.println(monsters + " " + a[i+1]);
                continue;
            }
            //System.out.println(b[i]);
            monsters += a[i];
            b[i] = b[i]-a[i];
            //System.out.println(b[i]);
            //System.out.println("monsters" + monsters);
            monsters += Math.min(a[i+1],b[i]);
            a[i+1] = Math.max(0,a[i+1]-b[i]);
            //System.out.println(monsters + " " + a[i+1]);
        } if(a[i]>=b[i]) {
                monsters += b[i];
                //System.out.println(monsters + " " + a[i+1]);
                continue;
            } a[i]>=b[i] a[i] a i b[i] b i {
                monsters += b[i];
                //System.out.println(monsters + " " + a[i+1]);
                continue;
            } monsters += b[i] monsters b[i] b i continue; monsters += a[i] monsters a[i] a i b[i] = b[i]-a[i] b[i] b i b[i]-a[i] b[i] b i a[i] a i monsters += Math.min(a[i+1],b[i]) monsters Math.min(a[i+1],b[i]) Math.min Math a[i+1] a i+1 i 1 b[i] b i a[i+1] = Math.max(0,a[i+1]-b[i]) a[i+1] a i+1 i 1 Math.max(0,a[i+1]-b[i]) Math.max Math 0 a[i+1]-b[i] a[i+1] a i+1 i 1 b[i] b i System.out.println(monsters) System.out.println System.out System System.out monsters String[] args args
import java.util.*;
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 monsters = 0;
        for(int i = 0; i<n; i++) {

            if(a[i]>=b[i]) {
                monsters += b[i];
                //System.out.println(monsters + " " + a[i+1]);
                continue;
            }
            //System.out.println(b[i]);
            monsters += a[i];
            b[i] = b[i]-a[i];
            //System.out.println(b[i]);
            //System.out.println("monsters" + monsters);
            monsters += Math.min(a[i+1],b[i]);
            a[i+1] = Math.max(0,a[i+1]-b[i]);
            //System.out.println(monsters + " " + a[i+1]);
        }
        System.out.println(monsters);
    }
}