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 ans = 0;
    for(int i = 0; i < n; i++) {
      if(a[i] >= b[i]) {
        ans += b[i];
      } else {
        ans += a[i];
        long r = b[i] - a[i];
        long t = Math.min(r, a[i + 1]);
        ans += t;
        a[i + 1] -= t;
      }
    }
    System.out.println(ans);
  }
} 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 ans = 0;
    for(int i = 0; i < n; i++) {
      if(a[i] >= b[i]) {
        ans += b[i];
      } else {
        ans += a[i];
        long r = b[i] - a[i];
        long t = Math.min(r, a[i + 1]);
        ans += t;
        a[i + 1] -= t;
      }
    }
    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];
    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 ans = 0;
    for(int i = 0; i < n; i++) {
      if(a[i] >= b[i]) {
        ans += b[i];
      } else {
        ans += a[i];
        long r = b[i] - a[i];
        long t = Math.min(r, a[i + 1]);
        ans += t;
        a[i + 1] -= t;
      }
    }
    System.out.println(ans);
  } 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 ans = 0;
    for(int i = 0; i < n; i++) {
      if(a[i] >= b[i]) {
        ans += b[i];
      } else {
        ans += a[i];
        long r = b[i] - a[i];
        long t = Math.min(r, a[i + 1]);
        ans += t;
        a[i + 1] -= t;
      }
    }
    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 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 ans = 0; ans 0 for(int i = 0; i < n; i++) {
      if(a[i] >= b[i]) {
        ans += b[i];
      } else {
        ans += a[i];
        long r = b[i] - a[i];
        long t = Math.min(r, a[i + 1]);
        ans += t;
        a[i + 1] -= t;
      }
    } 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];
        long r = b[i] - a[i];
        long t = Math.min(r, a[i + 1]);
        ans += t;
        a[i + 1] -= t;
      }
    } {
      if(a[i] >= b[i]) {
        ans += b[i];
      } else {
        ans += a[i];
        long r = b[i] - a[i];
        long t = Math.min(r, a[i + 1]);
        ans += t;
        a[i + 1] -= t;
      }
    } if(a[i] >= b[i]) {
        ans += b[i];
      } else {
        ans += a[i];
        long r = b[i] - a[i];
        long t = Math.min(r, a[i + 1]);
        ans += t;
        a[i + 1] -= t;
      } 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];
        long r = b[i] - a[i];
        long t = Math.min(r, a[i + 1]);
        ans += t;
        a[i + 1] -= t;
      } ans += a[i] ans a[i] a i long r = b[i] - a[i]; r b[i] - a[i] b[i] b i a[i] a i long t = Math.min(r, a[i + 1]); t Math.min(r, a[i + 1]) Math.min Math r a[i + 1] a i + 1 i 1 ans += t ans t a[i + 1] -= t a[i + 1] a i + 1 i 1 t 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];
    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 ans = 0;
    for(int i = 0; i < n; i++) {
      if(a[i] >= b[i]) {
        ans += b[i];
      } else {
        ans += a[i];
        long r = b[i] - a[i];
        long t = Math.min(r, a[i + 1]);
        ans += t;
        a[i + 1] -= t;
      }
    }
    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];
    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 ans = 0;
    for(int i = 0; i < n; i++) {
      if(a[i] >= b[i]) {
        ans += b[i];
      } else {
        ans += a[i];
        long r = b[i] - a[i];
        long t = Math.min(r, a[i + 1]);
        ans += t;
        a[i + 1] -= t;
      }
    }
    System.out.println(ans);
  }
} 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 ans = 0;
    for(int i = 0; i < n; i++) {
      if(a[i] >= b[i]) {
        ans += b[i];
      } else {
        ans += a[i];
        long r = b[i] - a[i];
        long t = Math.min(r, a[i + 1]);
        ans += t;
        a[i + 1] -= t;
      }
    }
    System.out.println(ans);
  }
}
