import java.util.*;
 
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];
        long b[] = new long[n];

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

        long sum = 0;

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

        System.out.println(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();
        long a[] = new long[n+1];
        long b[] = new long[n];

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

        long sum = 0;

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

        System.out.println(sum);
	}
} Main public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
        
        int n = sc.nextInt();
        long a[] = new long[n+1];
        long b[] = new long[n];

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

        long sum = 0;

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

        System.out.println(sum);
	} main {
		Scanner sc = new Scanner(System.in);
        
        int n = sc.nextInt();
        long a[] = new long[n+1];
        long b[] = new long[n];

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

        long sum = 0;

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

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

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

        long sum = 0;

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

        System.out.println(sum);
	}
} 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];
        long b[] = new long[n];

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

        long sum = 0;

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

        System.out.println(sum);
	}
} Main
import java.util.*;
 
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];
        long b[] = new long[n];

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

        long sum = 0;

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

        System.out.println(sum);
	}
}
