#include<bits/stdc++.h>
using namespace std;
int main()
{
int n;
cin >> n;
int a[n], b[n];
for(int i = 0; i < n; i ++)
cin >> a[i] >> b[i];
set<int> st;
for(int i = 0; i < n; i ++)
if(a[i])
st.insert(i);
set<pair<int,pair<int,int> > > sol;
for(int i = 0; i < n; i ++)
{
while(b[i])
{
int x = min(b[i], a[*st.begin()]);
a[*st.begin()] -= x;
b[i] -= x;
// cerr << x << ' ' << abs(i - *st.begin()) << endl;
sol.insert({i, {-abs(i - *st.begin()), x}});
if(!a[*st.begin()])
st.erase(st.begin());
}
}
long long ans = 0;
/* for(int i = n - 1; i >= 0; i--)
{
while(sol.size() && sol.rbegin()->first > i)
{
ans += -1ll * (sol.rbegin()->second.first) * (sol.rbegin()->second.second);
sol.erase(--sol.end());
}
while(a[i] > 0 && sol.size())
{
if(-sol.rbegin()->second.first < abs(i - sol.rbegin()->first))
{
int cnt = sol.rbegin()->second.second, idx = sol.rbegin()->first;
int x = min(cnt, a[i]), d = sol.rbegin()->second.first;
cerr << x << endl;
cerr << d << ' ' << abs(i - idx) << endl;
sol.erase(--sol.end());
cnt -= x;
a[i] -= x;
if(cnt > 0)
sol.insert({idx,{d, cnt}});
sol.insert({idx,{idx - i, x}});
}
else
break;
}
}*/
for(auto x : sol)
ans += -1ll * x.second.first * x.second.second;
cout << ans << endl;
return 0;
}
