#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

int nextInt(){
	int n=0 , ch=getchar();
	while( ch < '0' ) ch=getchar();
	while( ch >= '0' ) n = (n<<3)+(n<<1) + ch-'0', ch=getchar();
	return n;
}


static int G[100005];
static int C[100005];
static int da[100005];
static int a [100005];

int pianifica(int N, int M, int da[], int a[], int C[], int G[]);


int main(){
	assert(freopen("input.txt", "r", stdin));
	assert(freopen("output.txt", "w", stdout));
	
	int N = nextInt();
	int M = nextInt();
	
	int i;
	for(i=0; i<N; i++){
		G[i] = nextInt();
	}
	for(i=0; i<M; i++){
		C[i] = nextInt();
	}
	for(i=0; i<N-1; i++){
		da[i] = nextInt();
		a[i] = nextInt();
	}
	
	
	printf("%d\n", pianifica(N,M,da,a,C,G));
	
	fclose(stdin);
	fclose(stdout);
	
	return EXIT_SUCCESS;
}