include <bits/stdc++.h>

using namespace std;

struct node {

int x, y;

} p[100005];

bool cmp(node c, node d) {

return c.y < d.y;

}

int main() {

int n, len = -2147483647;
cin >> n;
for (int i = 1; i <= n; i++) {
	cin >> p[i].x >> p[i].y;
}
sort(p + 1, p + 1 + n);
int ans = 0;
for (int i = 1; i <= n; i++) {
	if (p[i].y > len) {
		ans += p[i].y - max(p[i].x, len) + 1;
		len = p[i].y + 1;
	}
}
cout << ans;

return 0;

}