#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<int, pii> pipii;
typedef pair<pii, int> piipi;
typedef pair<pii, pii> piipii;

#define mp make_pair
#define fi first
#define se second
#define all(a) (a).begin(), (a).end()
#define sz(a) (int)(a).size()
#define eb emplace_back

int x[10005], y[10005];
pii a[20005];

int val[20005];
struct twosat{
    int n;
    vector<vector<int> > adj, radj, scc;
    vector<int> sid, vis;
    stack<int> st;
    int cnt;

    void init(int m){
        n = m;
        adj.clear();
        radj.clear();
        sid.clear();
        vis.clear();
        scc.clear();

        adj.resize(m);
        radj.resize(m);
        sid.resize(m);
        vis.resize(m);
    }

    void impl(int x, int y){
        adj[x].push_back(y);
        radj[y].push_back(x);
    }
    void vee(int x, int y){
        impl(x^1, y);
        impl(y^1, x);
    }
    void nand(int x, int y){
        vee(x^1, y^1);
    }
    void xoro(int x, int y){
        vee(x, y);
        // vee(x^1, y^1);
    }

    void dfs1(int x){
        if(vis[x]++) return;
        for(int i=0;i<adj[x].size();i++) dfs1(adj[x][i]);
        st.push(x);
    }
    void dfs2(int x){
        if(!vis[x]) return;
        vis[x] = 0;
        sid[x] = cnt;
        scc.back().push_back(x);
        for(int i=0;i<radj[x].size();i++) dfs2(radj[x][i]);
    }
    bool two_sat(){
        cnt = 0;
        for(int i=0;i<n;i++) dfs1(i);
        while(!st.empty()){
            int v = st.top();
            st.pop();
            if(vis[v]){
                scc.push_back(vector<int>());
                dfs2(v);
                cnt++;
            }
        }
        for(int i=0;i<n;i+=2){
            if(sid[i] == sid[i+1]) return false;
        }
        return true;
    }
};

twosat sat;
void build(int n, int s, int e){
    if(s == e){
        val[s] = n;
        return;
    }
    else{
        int mid = (s+e)/2;
        build(n+n, s, mid);
        build(n+n+1, mid+1, e);
        sat.impl((n+n)*2, n*2);
        sat.impl((n+n+1)*2, n*2);
    }
}
void add(int n, int s, int e, int l, int r, int q){
    if(s > r || l > e) return;
    if(l <= s && e <= r){
        sat.nand(n*2, q*2);
        return;
    }
    int mid = (s+e)/2;
    add(n+n, s, mid, l, r, q);
    add(n+n+1, mid+1, e, l, r, q);
}
int idx[10005][2];
int main(){
    int n;
    scanf("%d", &n);
    for(int i=1;i<=n;i++){
        scanf("%d%d", &x[i], &y[i]);
        a[i] = mp(x[i], i);
        a[i+n] = mp(y[i], i);
    }
    sort(a+1, a+2*n+1);
    for(int i=1;i<=2*n;i++){
        if(idx[a[i].se][0] == 0) idx[a[i].se][0] = i;
        else idx[a[i].se][1] = i;
    }

    int lo = 1, hi = 1e9, ans = 0;
    while(lo <= hi){
        int mid = (lo+hi)/2;

        sat.init(16*n+2);
        build(1, 1, 2*n);

        int l = 1, r = 1;
        for(int i=1;i<=2*n;i++){
            l = min(l, i);
            r = max(r, i);
            while(a[i].fi-a[l].fi >= mid) l++;
            while(r+1 <= 2*n && a[r+1].fi-a[i].fi < mid) r++;

            if(i != l) add(1, 1, 2*n, l, i-1, val[i]);
            if(i != r) add(1, 1, 2*n, i+1, r, val[i]);
        }
        for(int i=1;i<=n;i++){
            int x = val[idx[i][0]], y = val[idx[i][1]];
            sat.xoro(x*2, y*2);
        }
        int ok = sat.two_sat();
        if(ok == 1) ans = mid, lo = mid+1;
        else hi = mid-1;
    }
    printf("%d\n", ans);
}

Measured memory_bytes: 43152