rt

#include<bits/stdc++.h>
using namespace std;
#define ll long long
ll n,m,ans,p; 
struct node{
	ll r,x;
}s[100009];
bool cmp(node s1,node s2)
{
	return s1.x<s1.x;
}
int main()
{
	cin>>m>>n;
	for(ll i=1;i<=n;i++)
	{
		cin>>s[i].x>>s[i].r;
		ans+=s[i].r;
	}
	sort(s+1,s+n+1,cmp);
	ans/=2;
	ll sum=0;
	for(ll i=1;i<=n;i++)
	{
		sum+=s[i].r;
		if(sum>=ans)
		{
			p=s[i].x;
			break;
		}
	}
	ans=0;
	for(ll i=1;i<=n;i++)
	{
		ans+=abs(p-s[i].x)*s[i].r;
	}
	cout<<ans;
	return 0;
 }