#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define rrep(i,n) for(int i = 1; i <= (n); ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define rng(a) a.begin(),a.end()
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vl;
typedef vector<P> vp;
#define dame { puts("-1"); return 0;}
#define yn {puts("Yes");}else{puts("No");}
#define MAX_N 200005

int main() {
    int n;
    cin >> n;
    int a[n];
    int b[n];
    int diff = 0;
    srep(i,1,n){
        cin >> a[i] >> b[i];
        diff += b[i] - a[i];
    }
    int c[n];
    int ans = 0;

    rep(i,1000005){
        a[0] = i;
        b[0] = i + diff;
        if(b[0] < 0) continue;
        int ma = 0;
        int sum = 0;
        rep(j,n){
            ma = max(ma, a[j]+b[j]);
            sum += a[j];
        }
        if(ma <= sum)ans++;
    }

    cout << ans << endl;
    return 0;
}