import java.util.*;

public class Main {
    public static void main(String args[]) throws Exception {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n+1];
        int[] b = new int[n];

        for(int i = 0; i <= n; i++)
        	a[i] = sc.nextInt();
        for(int i = 0; i < n; i++)
        	b[i] = sc.nextInt();
        
        long cnt = 0;
        for(int i = 0; i < n; i++) {
        	int cnt1 = Math.min(a[i], b[i]);
        	cnt += cnt1;
        	a[i] -= cnt1;
        	b[i] -= cnt1;
        	if(b[i] > 0) {
        		cnt1 = Math.min(b[i], a[i+1]);
        		cnt += cnt1;
        		a[i+1] -= cnt1;
        	}
        }
        System.out.println(cnt);
    }
} import java.util.*; util.* java public class Main {
    public static void main(String args[]) throws Exception {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n+1];
        int[] b = new int[n];

        for(int i = 0; i <= n; i++)
        	a[i] = sc.nextInt();
        for(int i = 0; i < n; i++)
        	b[i] = sc.nextInt();
        
        long cnt = 0;
        for(int i = 0; i < n; i++) {
        	int cnt1 = Math.min(a[i], b[i]);
        	cnt += cnt1;
        	a[i] -= cnt1;
        	b[i] -= cnt1;
        	if(b[i] > 0) {
        		cnt1 = Math.min(b[i], a[i+1]);
        		cnt += cnt1;
        		a[i+1] -= cnt1;
        	}
        }
        System.out.println(cnt);
    }
} Main public static void main(String args[]) throws Exception {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n+1];
        int[] b = new int[n];

        for(int i = 0; i <= n; i++)
        	a[i] = sc.nextInt();
        for(int i = 0; i < n; i++)
        	b[i] = sc.nextInt();
        
        long cnt = 0;
        for(int i = 0; i < n; i++) {
        	int cnt1 = Math.min(a[i], b[i]);
        	cnt += cnt1;
        	a[i] -= cnt1;
        	b[i] -= cnt1;
        	if(b[i] > 0) {
        		cnt1 = Math.min(b[i], a[i+1]);
        		cnt += cnt1;
        		a[i+1] -= cnt1;
        	}
        }
        System.out.println(cnt);
    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n+1];
        int[] b = new int[n];

        for(int i = 0; i <= n; i++)
        	a[i] = sc.nextInt();
        for(int i = 0; i < n; i++)
        	b[i] = sc.nextInt();
        
        long cnt = 0;
        for(int i = 0; i < n; i++) {
        	int cnt1 = Math.min(a[i], b[i]);
        	cnt += cnt1;
        	a[i] -= cnt1;
        	b[i] -= cnt1;
        	if(b[i] > 0) {
        		cnt1 = Math.min(b[i], a[i+1]);
        		cnt += cnt1;
        		a[i+1] -= cnt1;
        	}
        }
        System.out.println(cnt);
    } 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 for(int i = 0; i <= n; i++)
        	a[i] = sc.nextInt(); int i = 0; int i = 0; i 0 i <= n i n i++ i++ i 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] b i sc.nextInt() sc.nextInt sc long cnt = 0; cnt 0 for(int i = 0; i < n; i++) {
        	int cnt1 = Math.min(a[i], b[i]);
        	cnt += cnt1;
        	a[i] -= cnt1;
        	b[i] -= cnt1;
        	if(b[i] > 0) {
        		cnt1 = Math.min(b[i], a[i+1]);
        		cnt += cnt1;
        		a[i+1] -= cnt1;
        	}
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
        	int cnt1 = Math.min(a[i], b[i]);
        	cnt += cnt1;
        	a[i] -= cnt1;
        	b[i] -= cnt1;
        	if(b[i] > 0) {
        		cnt1 = Math.min(b[i], a[i+1]);
        		cnt += cnt1;
        		a[i+1] -= cnt1;
        	}
        } {
        	int cnt1 = Math.min(a[i], b[i]);
        	cnt += cnt1;
        	a[i] -= cnt1;
        	b[i] -= cnt1;
        	if(b[i] > 0) {
        		cnt1 = Math.min(b[i], a[i+1]);
        		cnt += cnt1;
        		a[i+1] -= cnt1;
        	}
        } int cnt1 = Math.min(a[i], b[i]); cnt1 Math.min(a[i], b[i]) Math.min Math a[i] a i b[i] b i cnt += cnt1 cnt cnt1 a[i] -= cnt1 a[i] a i cnt1 b[i] -= cnt1 b[i] b i cnt1 if(b[i] > 0) {
        		cnt1 = Math.min(b[i], a[i+1]);
        		cnt += cnt1;
        		a[i+1] -= cnt1;
        	} b[i] > 0 b[i] b i 0 {
        		cnt1 = Math.min(b[i], a[i+1]);
        		cnt += cnt1;
        		a[i+1] -= cnt1;
        	} cnt1 = Math.min(b[i], a[i+1]) cnt1 Math.min(b[i], a[i+1]) Math.min Math b[i] b i a[i+1] a i+1 i 1 cnt += cnt1 cnt cnt1 a[i+1] -= cnt1 a[i+1] a i+1 i 1 cnt1 System.out.println(cnt) System.out.println System.out System System.out cnt String args[] args public class Main {
    public static void main(String args[]) throws Exception {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n+1];
        int[] b = new int[n];

        for(int i = 0; i <= n; i++)
        	a[i] = sc.nextInt();
        for(int i = 0; i < n; i++)
        	b[i] = sc.nextInt();
        
        long cnt = 0;
        for(int i = 0; i < n; i++) {
        	int cnt1 = Math.min(a[i], b[i]);
        	cnt += cnt1;
        	a[i] -= cnt1;
        	b[i] -= cnt1;
        	if(b[i] > 0) {
        		cnt1 = Math.min(b[i], a[i+1]);
        		cnt += cnt1;
        		a[i+1] -= cnt1;
        	}
        }
        System.out.println(cnt);
    }
} public class Main {
    public static void main(String args[]) throws Exception {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n+1];
        int[] b = new int[n];

        for(int i = 0; i <= n; i++)
        	a[i] = sc.nextInt();
        for(int i = 0; i < n; i++)
        	b[i] = sc.nextInt();
        
        long cnt = 0;
        for(int i = 0; i < n; i++) {
        	int cnt1 = Math.min(a[i], b[i]);
        	cnt += cnt1;
        	a[i] -= cnt1;
        	b[i] -= cnt1;
        	if(b[i] > 0) {
        		cnt1 = Math.min(b[i], a[i+1]);
        		cnt += cnt1;
        		a[i+1] -= cnt1;
        	}
        }
        System.out.println(cnt);
    }
} Main
import java.util.*;

public class Main {
    public static void main(String args[]) throws Exception {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n+1];
        int[] b = new int[n];

        for(int i = 0; i <= n; i++)
        	a[i] = sc.nextInt();
        for(int i = 0; i < n; i++)
        	b[i] = sc.nextInt();
        
        long cnt = 0;
        for(int i = 0; i < n; i++) {
        	int cnt1 = Math.min(a[i], b[i]);
        	cnt += cnt1;
        	a[i] -= cnt1;
        	b[i] -= cnt1;
        	if(b[i] > 0) {
        		cnt1 = Math.min(b[i], a[i+1]);
        		cnt += cnt1;
        		a[i+1] -= cnt1;
        	}
        }
        System.out.println(cnt);
    }
}
