#include<bits/stdc++.h>
using namespace std;
int a[255];
int s[255];
int d[255];
int dp[255][255];
int main(){
	ios::sync_with_stdio(0);
	cin.tie(0), cout.tie(0);
	memset(dp,0x7f7f7f7f,sizeof(dp));
	int n,m;
	cin>>n>>m;
	for(int i=1;i<=n;i++){
		cin>>a[i];
	}
	for(int i=1;i<=m;i++){
		cin>>s[i]>>d[i];
	}
	dp[1][1]=0;
	for(int i=2;i<=n;i++){
		for(int j=m;j;j--){
			if(j>1&&s[j]>=a[i]&&s[j-1]>=a[i]){
				dp[i][j]=min(dp[i][j],dp[i][j-1]+1);
			}
			for(int k=1;k<=n;k++){
				if(d[j]>=i-k&&s[j]>=a[i]&&s[j]>=a[k]){
					dp[i][j]=min(dp[i][j],dp[k][j]);
				}
				if(j>1&&d[j-1]>=i-k&&s[j]>=a[i]&&s[j-1]>=a[i]&&s[j-1]>=a[k]){
					dp[i][j]=min(dp[i][j],dp[k][j-1]+1);
				}
			}
		}
	}
	int ans=0x7f7f7f7f;
	for(int i=1;i<=m;i++){
		ans=min(ans,dp[n][i]);
	}
	cout<<(ans==0x7f7f7f7f?-1:ans);
	return 0;
}