import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        // Your code here!
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n+1];
        int[] b = new int[n+1];
        long sum = 0;
        for (int i = 0; i <= n; i++) {
            a[i] = sc.nextInt();
            sum += a[i];
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }
        
        for (int i = 0; i < n; i++) {
            if (a[i] < b[i]) {
                b[i] -= a[i];
                a[i] = 0;
                
                if (a[i+1] < b[i]) {
                    a[i+1] = 0;
                } else {
                    a[i+1] -= b[i];
                }
            } else {
                a[i] -= b[i];
            }
        }
        
        long now = 0;
        for (int i = 0; i <= n; i++) {
            now += a[i];
        }
        
        System.out.println(sum - now);
    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args) throws Exception {
        // Your code here!
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n+1];
        int[] b = new int[n+1];
        long sum = 0;
        for (int i = 0; i <= n; i++) {
            a[i] = sc.nextInt();
            sum += a[i];
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }
        
        for (int i = 0; i < n; i++) {
            if (a[i] < b[i]) {
                b[i] -= a[i];
                a[i] = 0;
                
                if (a[i+1] < b[i]) {
                    a[i+1] = 0;
                } else {
                    a[i+1] -= b[i];
                }
            } else {
                a[i] -= b[i];
            }
        }
        
        long now = 0;
        for (int i = 0; i <= n; i++) {
            now += a[i];
        }
        
        System.out.println(sum - now);
    }
} Main public static void main(String[] args) throws Exception {
        // Your code here!
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n+1];
        int[] b = new int[n+1];
        long sum = 0;
        for (int i = 0; i <= n; i++) {
            a[i] = sc.nextInt();
            sum += a[i];
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }
        
        for (int i = 0; i < n; i++) {
            if (a[i] < b[i]) {
                b[i] -= a[i];
                a[i] = 0;
                
                if (a[i+1] < b[i]) {
                    a[i+1] = 0;
                } else {
                    a[i+1] -= b[i];
                }
            } else {
                a[i] -= b[i];
            }
        }
        
        long now = 0;
        for (int i = 0; i <= n; i++) {
            now += a[i];
        }
        
        System.out.println(sum - now);
    } main {
        // Your code here!
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n+1];
        int[] b = new int[n+1];
        long sum = 0;
        for (int i = 0; i <= n; i++) {
            a[i] = sc.nextInt();
            sum += a[i];
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }
        
        for (int i = 0; i < n; i++) {
            if (a[i] < b[i]) {
                b[i] -= a[i];
                a[i] = 0;
                
                if (a[i+1] < b[i]) {
                    a[i+1] = 0;
                } else {
                    a[i+1] -= b[i];
                }
            } else {
                a[i] -= b[i];
            }
        }
        
        long now = 0;
        for (int i = 0; i <= n; i++) {
            now += a[i];
        }
        
        System.out.println(sum - now);
    } 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+1]; b new int[n+1] n+1 n 1 long sum = 0; sum 0 for (int i = 0; i <= n; i++) {
            a[i] = sc.nextInt();
            sum += a[i];
        } int i = 0; int i = 0; i 0 i <= n i n i++ i++ i {
            a[i] = sc.nextInt();
            sum += a[i];
        } {
            a[i] = sc.nextInt();
            sum += a[i];
        } a[i] = sc.nextInt() a[i] a i sc.nextInt() sc.nextInt sc sum += a[i] sum a[i] a i 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 for (int i = 0; i < n; i++) {
            if (a[i] < b[i]) {
                b[i] -= a[i];
                a[i] = 0;
                
                if (a[i+1] < b[i]) {
                    a[i+1] = 0;
                } else {
                    a[i+1] -= b[i];
                }
            } else {
                a[i] -= b[i];
            }
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            if (a[i] < b[i]) {
                b[i] -= a[i];
                a[i] = 0;
                
                if (a[i+1] < b[i]) {
                    a[i+1] = 0;
                } else {
                    a[i+1] -= b[i];
                }
            } else {
                a[i] -= b[i];
            }
        } {
            if (a[i] < b[i]) {
                b[i] -= a[i];
                a[i] = 0;
                
                if (a[i+1] < b[i]) {
                    a[i+1] = 0;
                } else {
                    a[i+1] -= b[i];
                }
            } else {
                a[i] -= b[i];
            }
        } if (a[i] < b[i]) {
                b[i] -= a[i];
                a[i] = 0;
                
                if (a[i+1] < b[i]) {
                    a[i+1] = 0;
                } else {
                    a[i+1] -= b[i];
                }
            } else {
                a[i] -= b[i];
            } a[i] < b[i] a[i] a i b[i] b i {
                b[i] -= a[i];
                a[i] = 0;
                
                if (a[i+1] < b[i]) {
                    a[i+1] = 0;
                } else {
                    a[i+1] -= b[i];
                }
            } b[i] -= a[i] b[i] b i a[i] a i a[i] = 0 a[i] a i 0 if (a[i+1] < b[i]) {
                    a[i+1] = 0;
                } else {
                    a[i+1] -= b[i];
                } a[i+1] < b[i] a[i+1] a i+1 i 1 b[i] b i {
                    a[i+1] = 0;
                } a[i+1] = 0 a[i+1] a i+1 i 1 0 {
                    a[i+1] -= b[i];
                } a[i+1] -= b[i] a[i+1] a i+1 i 1 b[i] b i {
                a[i] -= b[i];
            } a[i] -= b[i] a[i] a i b[i] b i long now = 0; now 0 for (int i = 0; i <= n; i++) {
            now += a[i];
        } int i = 0; int i = 0; i 0 i <= n i n i++ i++ i {
            now += a[i];
        } {
            now += a[i];
        } now += a[i] now a[i] a i System.out.println(sum - now) System.out.println System.out System System.out sum - now sum now String[] args args public class Main {
    public static void main(String[] args) throws Exception {
        // Your code here!
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n+1];
        int[] b = new int[n+1];
        long sum = 0;
        for (int i = 0; i <= n; i++) {
            a[i] = sc.nextInt();
            sum += a[i];
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }
        
        for (int i = 0; i < n; i++) {
            if (a[i] < b[i]) {
                b[i] -= a[i];
                a[i] = 0;
                
                if (a[i+1] < b[i]) {
                    a[i+1] = 0;
                } else {
                    a[i+1] -= b[i];
                }
            } else {
                a[i] -= b[i];
            }
        }
        
        long now = 0;
        for (int i = 0; i <= n; i++) {
            now += a[i];
        }
        
        System.out.println(sum - now);
    }
} public class Main {
    public static void main(String[] args) throws Exception {
        // Your code here!
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n+1];
        int[] b = new int[n+1];
        long sum = 0;
        for (int i = 0; i <= n; i++) {
            a[i] = sc.nextInt();
            sum += a[i];
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }
        
        for (int i = 0; i < n; i++) {
            if (a[i] < b[i]) {
                b[i] -= a[i];
                a[i] = 0;
                
                if (a[i+1] < b[i]) {
                    a[i+1] = 0;
                } else {
                    a[i+1] -= b[i];
                }
            } else {
                a[i] -= b[i];
            }
        }
        
        long now = 0;
        for (int i = 0; i <= n; i++) {
            now += a[i];
        }
        
        System.out.println(sum - now);
    }
} Main
import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        // Your code here!
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n+1];
        int[] b = new int[n+1];
        long sum = 0;
        for (int i = 0; i <= n; i++) {
            a[i] = sc.nextInt();
            sum += a[i];
        }
        for (int i = 0; i < n; i++) {
            b[i] = sc.nextInt();
        }
        
        for (int i = 0; i < n; i++) {
            if (a[i] < b[i]) {
                b[i] -= a[i];
                a[i] = 0;
                
                if (a[i+1] < b[i]) {
                    a[i+1] = 0;
                } else {
                    a[i+1] -= b[i];
                }
            } else {
                a[i] -= b[i];
            }
        }
        
        long now = 0;
        for (int i = 0; i <= n; i++) {
            now += a[i];
        }
        
        System.out.println(sum - now);
    }
}
