// #pragma GCC optimize("O3", "unroll-loops")
// #pragma GCC target("avx2", "bmi", "bmi2", "lzcnt", "popcnt")

#include <bits/stdc++.h>
#define ldb long double
//#define double ldb
#define db double
#define unomap unordered_map
#define unoset unordered_set
#define endl '\n'
#define str string
#define strstr stringstream
#define sz(a) (int)a.size()
#define ll long long
// #define int ll
#define pii pair <int, int>
#define pll pair <ll, ll>
#define Unique(a) a.resize(unique(all(a)) - a.begin())
#define ull unsigned long long
#define fir first
#define sec second
#define idc cin.ignore()
#define lb lower_bound
#define ub upper_bound
#define all(s) s.begin(), s.end()
#define rall(s) s.rbegin(), s.rend()
#define rev reverse
#define gcd __gcd
#define pushb push_back
#define popb pop_back
#define pushf push_front
#define popf pop_front
#define emp emplace
#define empb emplace_back
#define empf emplace_front
#define mul2x(a, x) a << x
#define div2x(a, x) a >> x
#define lcm(a, b) (a / __gcd(a, b) * b)
#define log_base(x, base) log(x) / log(base)
#define debug cerr<<"No errors!",exit(0);
#define forw(i, a, b)  for (int i = a; i <= b; ++i)
#define forw2(i, a, b) for (ll i = a; i <= b; ++i)
#define fors(i, a, b)  for (int i = a; i >= b; --i)
#define fors2(i, a, b) for (ll i = a; i >= b; --i)
#define pqueue priority_queue
#define sqrt sqrtl
#define i128 __int128
#define popcount __builtin_popcountll
#define BIT(x, i) (((x) >> (i)) & 1)
#define MASK(x) ((1LL) << (x))
#define want_digit(x) cout << fixed << setprecision(x);
#define excuting_time 1000.0 * clock() / CLOCKS_PER_SEC
#define mapa make_pair
using namespace std;
const int MOD = 1e9 + 7; // 998244353
const int inf = 1e9;
const ll INF = 1e18; // MASK(63) - 1
const int limN = 1e5 + 5;

mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
inline ll random(const ll &L, const ll &R) {
    return uniform_int_distribution<ll> (L, R) (rng);
}

/* -------~~~~~~===== END OF TEMPLATE =====~~~~~~------- */

int n;
pii v[limN];
inline void solve() {
    cin >> n;
    forw (i, 1, n) cin >> v[i].fir >> v[i].sec;
    sort(v + 1, v + n + 1);
    int lim = 0, ans = 0;
    forw (i, 1, n) {
        ans += max(0, v[i].sec - lim - 1);
        lim = max(lim, v[i].sec);
    }
    cout << ans << endl;
}

signed main() {
    ios::sync_with_stdio(false), cin.tie(nullptr);
    srand(time(NULL));
    #define name "test"
    if (fopen(name".INP", "r")) {
        freopen(name".INP", "r", stdin);
        freopen(name".OUT", "w", stdout);
    }
    bool testCase = false;
    int numTest = 1;
    // cin >> numTest;
    forw (i, 1, numTest) {
        if (testCase) cout << "Case #" << i << ": ";
        solve();
    }
    return 0;
}