#include <iostream>
using namespace std;
const int N = 1<<20;
long long Pre[N], Suf[N], Pct[N], Sct[N], a[N], b[N];
int main(){
long long n, Ans = 1e18, Sum = 0;
cin>>n;
for (int i=1;i<=n;i++){
cin>>a[i]>>b[i];
int k = min(a[i], b[i]);
a[i] -= k, b[i] -= k;
Sum += a[i];
}
for (int i=1;i<=n;i++){
Pre[i] = Pre[i-1] + a[i] - b[i];
Pct[i] = Pct[i-1] + abs(Pre[i]);
}
for (int i=n;i>=1;i--){
Suf[i] = Suf[i+1] + a[i] - b[i];
Sct[i] = Sct[i+1] + abs(Suf[i]);
}
for (int i=1;i<=n;i++){
if (a[i] > 0)
Ans = min(Ans, Pct[i-1] + Sct[i+1] + abs(a[i] - b[i] - 1));
}
if (Pre[n])
cout<<Ans<<'\n';
else
cout<<Pct[n]<<'\n';
}
