import java.io.*;
import java.util.*;
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        PrintWriter out = new PrintWriter(System.out);
        
        final 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 ans = 0;
        
        for (int i = 0; i < N; i++) {
            if (a[i] >= b[i]) {
                ans += b[i];
            } else if (a[i] < b[i] && a[i+1] >= b[i] - a[i]) {
                ans += b[i];
                a[i+1] -= (b[i] - a[i]);
            } else if (a[i] < b[i] && a[i+1] < b[i] - a[i]) {
                ans += (a[i] + a[i+1]);
                a[i+1] = 0;
            }
        }
        
        out.println(ans);
        
        out.flush();
    }
} import java.io.*; io.* java import java.util.*; util.* java public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        PrintWriter out = new PrintWriter(System.out);
        
        final 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 ans = 0;
        
        for (int i = 0; i < N; i++) {
            if (a[i] >= b[i]) {
                ans += b[i];
            } else if (a[i] < b[i] && a[i+1] >= b[i] - a[i]) {
                ans += b[i];
                a[i+1] -= (b[i] - a[i]);
            } else if (a[i] < b[i] && a[i+1] < b[i] - a[i]) {
                ans += (a[i] + a[i+1]);
                a[i+1] = 0;
            }
        }
        
        out.println(ans);
        
        out.flush();
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        PrintWriter out = new PrintWriter(System.out);
        
        final 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 ans = 0;
        
        for (int i = 0; i < N; i++) {
            if (a[i] >= b[i]) {
                ans += b[i];
            } else if (a[i] < b[i] && a[i+1] >= b[i] - a[i]) {
                ans += b[i];
                a[i+1] -= (b[i] - a[i]);
            } else if (a[i] < b[i] && a[i+1] < b[i] - a[i]) {
                ans += (a[i] + a[i+1]);
                a[i+1] = 0;
            }
        }
        
        out.println(ans);
        
        out.flush();
    } main {
        Scanner sc = new Scanner(System.in);
        PrintWriter out = new PrintWriter(System.out);
        
        final 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 ans = 0;
        
        for (int i = 0; i < N; i++) {
            if (a[i] >= b[i]) {
                ans += b[i];
            } else if (a[i] < b[i] && a[i+1] >= b[i] - a[i]) {
                ans += b[i];
                a[i+1] -= (b[i] - a[i]);
            } else if (a[i] < b[i] && a[i+1] < b[i] - a[i]) {
                ans += (a[i] + a[i+1]);
                a[i+1] = 0;
            }
        }
        
        out.println(ans);
        
        out.flush();
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) PrintWriter out = new PrintWriter(System.out); out new PrintWriter(System.out) final 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 ans = 0; ans 0 for (int i = 0; i < N; i++) {
            if (a[i] >= b[i]) {
                ans += b[i];
            } else if (a[i] < b[i] && a[i+1] >= b[i] - a[i]) {
                ans += b[i];
                a[i+1] -= (b[i] - a[i]);
            } else if (a[i] < b[i] && a[i+1] < b[i] - a[i]) {
                ans += (a[i] + a[i+1]);
                a[i+1] = 0;
            }
        } int i = 0; int i = 0; i 0 i < N i N i++ i++ i {
            if (a[i] >= b[i]) {
                ans += b[i];
            } else if (a[i] < b[i] && a[i+1] >= b[i] - a[i]) {
                ans += b[i];
                a[i+1] -= (b[i] - a[i]);
            } else if (a[i] < b[i] && a[i+1] < b[i] - a[i]) {
                ans += (a[i] + a[i+1]);
                a[i+1] = 0;
            }
        } {
            if (a[i] >= b[i]) {
                ans += b[i];
            } else if (a[i] < b[i] && a[i+1] >= b[i] - a[i]) {
                ans += b[i];
                a[i+1] -= (b[i] - a[i]);
            } else if (a[i] < b[i] && a[i+1] < b[i] - a[i]) {
                ans += (a[i] + a[i+1]);
                a[i+1] = 0;
            }
        } if (a[i] >= b[i]) {
                ans += b[i];
            } else if (a[i] < b[i] && a[i+1] >= b[i] - a[i]) {
                ans += b[i];
                a[i+1] -= (b[i] - a[i]);
            } else if (a[i] < b[i] && a[i+1] < b[i] - a[i]) {
                ans += (a[i] + a[i+1]);
                a[i+1] = 0;
            } a[i] >= b[i] a[i] a i b[i] b i {
                ans += b[i];
            } ans += b[i] ans b[i] b i if (a[i] < b[i] && a[i+1] >= b[i] - a[i]) {
                ans += b[i];
                a[i+1] -= (b[i] - a[i]);
            } else if (a[i] < b[i] && a[i+1] < b[i] - a[i]) {
                ans += (a[i] + a[i+1]);
                a[i+1] = 0;
            } a[i] < b[i] && a[i+1] >= b[i] - a[i] a[i] < b[i] a[i] a i b[i] b i 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 {
                ans += b[i];
                a[i+1] -= (b[i] - a[i]);
            } ans += b[i] ans b[i] b i 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] < b[i] && a[i+1] < b[i] - a[i]) {
                ans += (a[i] + a[i+1]);
                a[i+1] = 0;
            } a[i] < b[i] && a[i+1] < b[i] - a[i] a[i] < b[i] a[i] a i b[i] b i 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 {
                ans += (a[i] + a[i+1]);
                a[i+1] = 0;
            } ans += (a[i] + a[i+1]) ans (a[i] + a[i+1]) a[i] a i a[i+1] a i+1 i 1 a[i+1] = 0 a[i+1] a i+1 i 1 0 out.println(ans) out.println out ans out.flush() out.flush out String[] args args public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        PrintWriter out = new PrintWriter(System.out);
        
        final 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 ans = 0;
        
        for (int i = 0; i < N; i++) {
            if (a[i] >= b[i]) {
                ans += b[i];
            } else if (a[i] < b[i] && a[i+1] >= b[i] - a[i]) {
                ans += b[i];
                a[i+1] -= (b[i] - a[i]);
            } else if (a[i] < b[i] && a[i+1] < b[i] - a[i]) {
                ans += (a[i] + a[i+1]);
                a[i+1] = 0;
            }
        }
        
        out.println(ans);
        
        out.flush();
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        PrintWriter out = new PrintWriter(System.out);
        
        final 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 ans = 0;
        
        for (int i = 0; i < N; i++) {
            if (a[i] >= b[i]) {
                ans += b[i];
            } else if (a[i] < b[i] && a[i+1] >= b[i] - a[i]) {
                ans += b[i];
                a[i+1] -= (b[i] - a[i]);
            } else if (a[i] < b[i] && a[i+1] < b[i] - a[i]) {
                ans += (a[i] + a[i+1]);
                a[i+1] = 0;
            }
        }
        
        out.println(ans);
        
        out.flush();
    }
} Main
import java.io.*;
import java.util.*;
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        PrintWriter out = new PrintWriter(System.out);
        
        final 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 ans = 0;
        
        for (int i = 0; i < N; i++) {
            if (a[i] >= b[i]) {
                ans += b[i];
            } else if (a[i] < b[i] && a[i+1] >= b[i] - a[i]) {
                ans += b[i];
                a[i+1] -= (b[i] - a[i]);
            } else if (a[i] < b[i] && a[i+1] < b[i] - a[i]) {
                ans += (a[i] + a[i+1]);
                a[i+1] = 0;
            }
        }
        
        out.println(ans);
        
        out.flush();
    }
}