import java.util.*;

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

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