#include<bits/stdc++.h>
using namespace std;
#define rep(i,x,y) for(int i=x;i<y;i++)
#define range(a) (a).begin(),(a).end()
#define print(A,n) rep(i,0,n){cout<<(i ? " ":"")<<A[i];}cout<<endl;
#define pprint(A,m,n) rep(j,0,m){print(A[j],n);}
const long mod=1e9+7;
const int size=1e5;
const int INF=1e9;
int main(){
	int N;cin>>N;
	int a=0,b=0;int A[N],B[N];
	rep(i,1,N){
		cin>>A[i]>>B[i];
		a+=A[i];b+=B[i];
	}A[0]=0;B[0]=0;
	rep(i,1,N){
		A[0]=max(A[0],A[i]+B[i]-a);
		B[0]=max(B[0],A[i]+B[i]-b);
	}cout<<min(b-A[0],a-B[0])+1<<endl;
    //cout<<A[0]<<B[0]<<endl;
}