#include<iostream>

 #include<cstdio>

 #include<cstring>

 #include<algorithm>

 #define re register

 using namespace std;

 int max(int a,int b){return a>b?a:b;}

 struct data{

     int t,dl;

     bool operator < (const data &tmp) const{return dl>tmp.dl;}

 }a[];

 int n,tt,ans;

 int main(){

     scanf("%d",&n);

     for(re int i=;i<=n;++i) scanf("%d%d",&a[i].t,&a[i].dl);

     sort(a+,a+n+); tt=a[].dl;

     for(re int i=;i<=n;++i){

         tt=min(tt,a[i].dl); tt-=a[i].t;//注意在deadline前完成所以要取min

     }tt< ? printf("-1"):printf("%d",tt);

     return ;

 }