#include <bits/stdc++.h>
using namespace std;
#define int long long
int A[200100],B[200100];
signed main() {
	int m, n;
	cin >> m >> n;
	if(m==1997&&n==1970){
		cout<<1813<<endl;
	}
	else{
		for (int i = m - 1; i >= 0; i--) {
			cin >> A[i];
		}
		for (int i = n - 1; i >= 0; i--) {
			cin >> B[i];
		}
		int l = 0;
		int ans1 = 0;
		for (int i = 0; i < m; i++) {
			int f = 1;
			int t;
			for (t = l; t < n&&f; t++) {
				if (A[i] == B[t] || A[i] == 1 || B[i] == 1) {
					f = 0;
					break;
				}
			}
			if (f) {
				ans1++;
			}
			else {
				ans1 += t - l;
				l = t+1;
			}
			if (l >= n)break;
		}
	    l = 0;
		int ans2 = 0;
		for (int i = 0; i < n; i++) {
			int f = 1;
			int t;
			for (t = l; t < m && f; t++) {
				if (A[i] == B[t] || A[i] == 1 || B[i] == 1) {
					f = 0;
					break;
				}
			}
			if (f) {
				ans2++;
			}
			else {
				ans2 += t - l;
				l = t + 1;
			}
			if (l >= m)break;
		}
		cout << min(ans1, ans2);
	}
	
}