#include <bits/stdc++.h>
using namespace std;
#define ll long long
int seg[4000000];
int laz[4000000];
int a[4000003];
int z;
int b[4000003];
int ans=0;
int n;
void merg(int v,int v1,int v2)
{
seg[v]=max(seg[v1],seg[v2]);
}
void build(int v,int tl,int tr)
{
if(tl==tr)
{
seg[v]=a[tl];
return ;
}
int tm=(tl+tr)/2;
build(v*2,tl,tm);
build(v*2+1,tm+1,tr);
merg(v,v*2,v*2+1);
}
void push(int v)
{
laz[v*2]+=laz[v];
seg[v*2]+=laz[v];
seg[v*2+1]+=laz[v];
laz[v*2+1]+=laz[v];
laz[v]=0;
}
void update(int v,int tl,int tr,int l,int r)
{
if(l>r)
return ;
if(tl==l&&tr==r)
{
seg[v]++;
laz[v]++;
return ;
}
push(v);
int tm=(tl+tr)>>1;
update(v*2,tl,tm,l,min(r,tm));
update(v*2+1,tm+1,tr,max(tm+1,l),r);
merg(v,v*2,v*2+1);
}
int get1(int v,int tl,int tr,int pos)
{
// cout<<tl<<' '<<tr<<' '<<pos<<endl;
if(pos<tl||pos>tr)
return 1500000000;
if(tl==tr)
return seg[v];
int tm=(tl+tr)>>1;
push(v);
return min(get1(v*2,tl,tm,pos),get1(v*2+1,tm+1,tr,pos));
}
int get(int v,int l,int r,int val)
{
//cout<<tl<<' '<<tr<<endl;
/* if(val<tl||val>tr)
return 1000000;*/
// cout<<tl<<' '<<tr<<endl;
l--;
while(l+1<r)
{int m=(l+r)/2;
if(get1(1,0,150000,m)<val)
l=m;
else
r=m;
}
if(get1(1,0,150000,150000)<val)
return 150001;
else
return r;
}
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
// freopen("balancing.in","r",stdin);
// freopen("balancing.out","w",stdout);
cin>>n;
int q;
pair<int,int>h[n];
for(int i=0;i<n;i++)
{
cin>>h[i].first>>h[i].second;
}
sort(h,h+n);
for(int i=0;i<n;i++)
{
int height=h[i].first;
int number=h[i].second;
int st=150000-height+1;
int en=st+number-1;
int valen=get1(1,0,150000,en);
int nos=get(1,st,150000,valen);
int noe=get(1,st,150000,valen+1);
// cout<<valen<<' '<<nos<<' '<<noe<<endl;
update(1,0,150000,st,nos-1);
int left=number-(nos-st);
update(1,0,150000,noe-left,noe-1);
/*for(int y=st;y<=150000;y++)
{
cout<<get1(1,0,150000,y)<<' ';
}
cout<<endl;*/
}
ll ans=0;
for(int i=0;i<=150000;i++)
{
ll p=get1(1,0,150000,i);
if(p>0)
// cout<<p<<endl;
ans+=(p)*(p-1)/2;
}
cout<<ans<<endl;
}
