import java.util.Scanner;
import java.util.HashMap;
import java.util.List;
import java.util.Arrays;
import java.util.ArrayList;
import java.lang.Math;

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];
        for (int i = 0; i < n+1; i++) {
            a[i] = sc.nextLong();
        }
        long[] b = new long[n];
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextLong();
        }
        long ans = 0;
        for (int i = 0; i < n; i++) {
            if (a[i] >= b[i]) {
                ans += b[i];
            } else {
                ans += a[i];
                b[i] -= a[i];
                if (b[i] >= a[i+1]) {
                    ans += a[i+1];
                    a[i+1] = 0;
                } else {
                    a[i+1] -= b[i];
                    ans += b[i];
                }
            }
        }
        System.out.println(ans);
    }

} import java.util.Scanner; Scanner java.util import java.util.HashMap; HashMap java.util import java.util.List; List java.util import java.util.Arrays; Arrays java.util import java.util.ArrayList; ArrayList java.util import java.lang.Math; Math java.lang 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];
        for (int i = 0; i < n+1; i++) {
            a[i] = sc.nextLong();
        }
        long[] b = new long[n];
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextLong();
        }
        long ans = 0;
        for (int i = 0; i < n; i++) {
            if (a[i] >= b[i]) {
                ans += b[i];
            } else {
                ans += a[i];
                b[i] -= a[i];
                if (b[i] >= a[i+1]) {
                    ans += a[i+1];
                    a[i+1] = 0;
                } else {
                    a[i+1] -= b[i];
                    ans += b[i];
                }
            }
        }
        System.out.println(ans);
    }

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

} 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];
        for (int i = 0; i < n+1; i++) {
            a[i] = sc.nextLong();
        }
        long[] b = new long[n];
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextLong();
        }
        long ans = 0;
        for (int i = 0; i < n; i++) {
            if (a[i] >= b[i]) {
                ans += b[i];
            } else {
                ans += a[i];
                b[i] -= a[i];
                if (b[i] >= a[i+1]) {
                    ans += a[i+1];
                    a[i+1] = 0;
                } else {
                    a[i+1] -= b[i];
                    ans += b[i];
                }
            }
        }
        System.out.println(ans);
    }

} Main
import java.util.Scanner;
import java.util.HashMap;
import java.util.List;
import java.util.Arrays;
import java.util.ArrayList;
import java.lang.Math;

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];
        for (int i = 0; i < n+1; i++) {
            a[i] = sc.nextLong();
        }
        long[] b = new long[n];
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextLong();
        }
        long ans = 0;
        for (int i = 0; i < n; i++) {
            if (a[i] >= b[i]) {
                ans += b[i];
            } else {
                ans += a[i];
                b[i] -= a[i];
                if (b[i] >= a[i+1]) {
                    ans += a[i+1];
                    a[i+1] = 0;
                } else {
                    a[i+1] -= b[i];
                    ans += b[i];
                }
            }
        }
        System.out.println(ans);
    }

}
