#include<bits/stdc++.h>
using namespace std;
#define int long long
int n,t;
struct node
{
	int d,b;
}a[100010];
bool cmp(node g,node h)
{
	return g.d<h.d;
}
signed main()
{
	cin>>n>>t;
	for(int i=1;i<=n;i++)
	{
		cin>>a[i].d>>a[i].b;
	}
	sort(a+1,a+n+1,cmp);
	int sum=0;
	for(int i=1;i<=n;i++)
	{
		if(sum>=t)
		{
			cout<<t<<endl;
			return 0;
		}
		if(a[i].d>t) break;
		else if(a[i].d==t) 
		{
			if(a[i].b!=0) sum+=1;
			break;
		}
		else sum+=a[i].b;
	} 
	cout<<sum<<endl;
	return 0;
}