#include<iostream>

#include<algorithm>

#include<cstdio>

using namespace std; 

const int MAXN=;

inline int rd(){

    int ret=,f=;char c;

    while(c=getchar(),!isdigit(c))f=c=='-'?-:;

    while(isdigit(c))ret=ret*+c-'',c=getchar();

    return ret*f;

}

struct Node{

    int lon,tim;

}nodes[MAXN];

bool cmp(const Node &x,const Node &y){

    return x.tim<y.tim;

}

int n;

int main(){

//    freopen("manage.in","r",stdin);

//    freopen("manage.out","w",stdout);

    n=rd();

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

        nodes[i].lon = rd();

        nodes[i].tim = rd();

    }

    sort(nodes+,nodes++n,cmp);

    long long sum=,mn=(<<),v;

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

        sum+=nodes[i].lon;

        v=nodes[i].tim-sum;

        if(v<) return puts("-1"),;

        mn=min(mn,v);

    }

    printf("%lld",mn);

    return ;

}