import java.util.*;
import java.util.Collections;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        long[] a = new long[N+1];
        long[] b = new long[N];
        
        for(int i = 0; i < N+1; i++) {
            a[i] = Long.parseLong(sc.next());
        }
        
        for(int i = 0; i < N; i++) {
            b[i] = Long.parseLong(sc.next());
        }
        
        long count = 0;
        
        for(int i = 1; i < N+1; i ++) {
            if(a[i-1] >= b[i-1]) {
                a[i-1] -= b[i-1];
                count += b[i-1];
            }else {
                if(a[i] >= b[i-1] - a[i-1]) {
                    count += b[i-1];
                    a[i] -= b[i-1] - a[i-1];
                    a[i-1] = 0;
                }else {
                    count += a[i-1] + a[i];
                    a[i-1] = 0;
                    a[i] = 0;
                }
            }
            
        }
        
        System.out.println(count);
        
    }
} import java.util.*; util.* java import java.util.Collections; Collections java.util public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        long[] a = new long[N+1];
        long[] b = new long[N];
        
        for(int i = 0; i < N+1; i++) {
            a[i] = Long.parseLong(sc.next());
        }
        
        for(int i = 0; i < N; i++) {
            b[i] = Long.parseLong(sc.next());
        }
        
        long count = 0;
        
        for(int i = 1; i < N+1; i ++) {
            if(a[i-1] >= b[i-1]) {
                a[i-1] -= b[i-1];
                count += b[i-1];
            }else {
                if(a[i] >= b[i-1] - a[i-1]) {
                    count += b[i-1];
                    a[i] -= b[i-1] - a[i-1];
                    a[i-1] = 0;
                }else {
                    count += a[i-1] + a[i];
                    a[i-1] = 0;
                    a[i] = 0;
                }
            }
            
        }
        
        System.out.println(count);
        
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        long[] a = new long[N+1];
        long[] b = new long[N];
        
        for(int i = 0; i < N+1; i++) {
            a[i] = Long.parseLong(sc.next());
        }
        
        for(int i = 0; i < N; i++) {
            b[i] = Long.parseLong(sc.next());
        }
        
        long count = 0;
        
        for(int i = 1; i < N+1; i ++) {
            if(a[i-1] >= b[i-1]) {
                a[i-1] -= b[i-1];
                count += b[i-1];
            }else {
                if(a[i] >= b[i-1] - a[i-1]) {
                    count += b[i-1];
                    a[i] -= b[i-1] - a[i-1];
                    a[i-1] = 0;
                }else {
                    count += a[i-1] + a[i];
                    a[i-1] = 0;
                    a[i] = 0;
                }
            }
            
        }
        
        System.out.println(count);
        
    } main {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        long[] a = new long[N+1];
        long[] b = new long[N];
        
        for(int i = 0; i < N+1; i++) {
            a[i] = Long.parseLong(sc.next());
        }
        
        for(int i = 0; i < N; i++) {
            b[i] = Long.parseLong(sc.next());
        }
        
        long count = 0;
        
        for(int i = 1; i < N+1; i ++) {
            if(a[i-1] >= b[i-1]) {
                a[i-1] -= b[i-1];
                count += b[i-1];
            }else {
                if(a[i] >= b[i-1] - a[i-1]) {
                    count += b[i-1];
                    a[i] -= b[i-1] - a[i-1];
                    a[i-1] = 0;
                }else {
                    count += a[i-1] + a[i];
                    a[i-1] = 0;
                    a[i] = 0;
                }
            }
            
        }
        
        System.out.println(count);
        
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int N = Integer.parseInt(sc.next()); N Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next 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] = Long.parseLong(sc.next());
        } int i = 0; int i = 0; i 0 i < N+1 i N+1 N 1 i++ i++ i {
            a[i] = Long.parseLong(sc.next());
        } {
            a[i] = Long.parseLong(sc.next());
        } a[i] = Long.parseLong(sc.next()) a[i] a i Long.parseLong(sc.next()) Long.parseLong Long sc.next() sc.next sc for(int i = 0; i < N; i++) {
            b[i] = Long.parseLong(sc.next());
        } int i = 0; int i = 0; i 0 i < N i N i++ i++ i {
            b[i] = Long.parseLong(sc.next());
        } {
            b[i] = Long.parseLong(sc.next());
        } b[i] = Long.parseLong(sc.next()) b[i] b i Long.parseLong(sc.next()) Long.parseLong Long sc.next() sc.next sc long count = 0; count 0 for(int i = 1; i < N+1; i ++) {
            if(a[i-1] >= b[i-1]) {
                a[i-1] -= b[i-1];
                count += b[i-1];
            }else {
                if(a[i] >= b[i-1] - a[i-1]) {
                    count += b[i-1];
                    a[i] -= b[i-1] - a[i-1];
                    a[i-1] = 0;
                }else {
                    count += a[i-1] + a[i];
                    a[i-1] = 0;
                    a[i] = 0;
                }
            }
            
        } int i = 1; int i = 1; i 1 i < N+1 i N+1 N 1 i ++ i ++ i {
            if(a[i-1] >= b[i-1]) {
                a[i-1] -= b[i-1];
                count += b[i-1];
            }else {
                if(a[i] >= b[i-1] - a[i-1]) {
                    count += b[i-1];
                    a[i] -= b[i-1] - a[i-1];
                    a[i-1] = 0;
                }else {
                    count += a[i-1] + a[i];
                    a[i-1] = 0;
                    a[i] = 0;
                }
            }
            
        } {
            if(a[i-1] >= b[i-1]) {
                a[i-1] -= b[i-1];
                count += b[i-1];
            }else {
                if(a[i] >= b[i-1] - a[i-1]) {
                    count += b[i-1];
                    a[i] -= b[i-1] - a[i-1];
                    a[i-1] = 0;
                }else {
                    count += a[i-1] + a[i];
                    a[i-1] = 0;
                    a[i] = 0;
                }
            }
            
        } if(a[i-1] >= b[i-1]) {
                a[i-1] -= b[i-1];
                count += b[i-1];
            }else {
                if(a[i] >= b[i-1] - a[i-1]) {
                    count += b[i-1];
                    a[i] -= b[i-1] - a[i-1];
                    a[i-1] = 0;
                }else {
                    count += a[i-1] + a[i];
                    a[i-1] = 0;
                    a[i] = 0;
                }
            } a[i-1] >= b[i-1] a[i-1] a i-1 i 1 b[i-1] b i-1 i 1 {
                a[i-1] -= b[i-1];
                count += b[i-1];
            } a[i-1] -= b[i-1] a[i-1] a i-1 i 1 b[i-1] b i-1 i 1 count += b[i-1] count b[i-1] b i-1 i 1 {
                if(a[i] >= b[i-1] - a[i-1]) {
                    count += b[i-1];
                    a[i] -= b[i-1] - a[i-1];
                    a[i-1] = 0;
                }else {
                    count += a[i-1] + a[i];
                    a[i-1] = 0;
                    a[i] = 0;
                }
            } if(a[i] >= b[i-1] - a[i-1]) {
                    count += b[i-1];
                    a[i] -= b[i-1] - a[i-1];
                    a[i-1] = 0;
                }else {
                    count += a[i-1] + a[i];
                    a[i-1] = 0;
                    a[i] = 0;
                } a[i] >= b[i-1] - a[i-1] a[i] a i b[i-1] - a[i-1] b[i-1] b i-1 i 1 a[i-1] a i-1 i 1 {
                    count += b[i-1];
                    a[i] -= b[i-1] - a[i-1];
                    a[i-1] = 0;
                } count += b[i-1] count b[i-1] b i-1 i 1 a[i] -= b[i-1] - a[i-1] a[i] a i b[i-1] - a[i-1] b[i-1] b i-1 i 1 a[i-1] a i-1 i 1 a[i-1] = 0 a[i-1] a i-1 i 1 0 {
                    count += a[i-1] + a[i];
                    a[i-1] = 0;
                    a[i] = 0;
                } count += a[i-1] + a[i] count a[i-1] + a[i] a[i-1] a i-1 i 1 a[i] a i a[i-1] = 0 a[i-1] a i-1 i 1 0 a[i] = 0 a[i] a i 0 System.out.println(count) System.out.println System.out System System.out count String[] args args public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        long[] a = new long[N+1];
        long[] b = new long[N];
        
        for(int i = 0; i < N+1; i++) {
            a[i] = Long.parseLong(sc.next());
        }
        
        for(int i = 0; i < N; i++) {
            b[i] = Long.parseLong(sc.next());
        }
        
        long count = 0;
        
        for(int i = 1; i < N+1; i ++) {
            if(a[i-1] >= b[i-1]) {
                a[i-1] -= b[i-1];
                count += b[i-1];
            }else {
                if(a[i] >= b[i-1] - a[i-1]) {
                    count += b[i-1];
                    a[i] -= b[i-1] - a[i-1];
                    a[i-1] = 0;
                }else {
                    count += a[i-1] + a[i];
                    a[i-1] = 0;
                    a[i] = 0;
                }
            }
            
        }
        
        System.out.println(count);
        
    }
} public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        long[] a = new long[N+1];
        long[] b = new long[N];
        
        for(int i = 0; i < N+1; i++) {
            a[i] = Long.parseLong(sc.next());
        }
        
        for(int i = 0; i < N; i++) {
            b[i] = Long.parseLong(sc.next());
        }
        
        long count = 0;
        
        for(int i = 1; i < N+1; i ++) {
            if(a[i-1] >= b[i-1]) {
                a[i-1] -= b[i-1];
                count += b[i-1];
            }else {
                if(a[i] >= b[i-1] - a[i-1]) {
                    count += b[i-1];
                    a[i] -= b[i-1] - a[i-1];
                    a[i-1] = 0;
                }else {
                    count += a[i-1] + a[i];
                    a[i-1] = 0;
                    a[i] = 0;
                }
            }
            
        }
        
        System.out.println(count);
        
    }
} Main
import java.util.*;
import java.util.Collections;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        long[] a = new long[N+1];
        long[] b = new long[N];
        
        for(int i = 0; i < N+1; i++) {
            a[i] = Long.parseLong(sc.next());
        }
        
        for(int i = 0; i < N; i++) {
            b[i] = Long.parseLong(sc.next());
        }
        
        long count = 0;
        
        for(int i = 1; i < N+1; i ++) {
            if(a[i-1] >= b[i-1]) {
                a[i-1] -= b[i-1];
                count += b[i-1];
            }else {
                if(a[i] >= b[i-1] - a[i-1]) {
                    count += b[i-1];
                    a[i] -= b[i-1] - a[i-1];
                    a[i-1] = 0;
                }else {
                    count += a[i-1] + a[i];
                    a[i-1] = 0;
                    a[i] = 0;
                }
            }
            
        }
        
        System.out.println(count);
        
    }
}