#include <iostream>
using namespace std;
int main()
{
    int num;
    int n1,n2;
    cin >> num;
    int nums[num*2];
    int i = 0;
    int max = 0;
    int min = 0;
    int first = 1;
    int count = 0;
    while(num--)
    {
        cin >> n1 >> n2;
        if(first)
        {
            min = n1;
            max = n2;
            first = 0;
        }
        if(min > max)
            count += (min - max) - 1;
        if(n2 > max)
            max = n2;
        if(min > n2)
            count += (min - n2) - 1;
        if(n1 < min)
            min = n1;
    }
    cout << count;
}

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

NAoxIDMKMiA2CjggMTAKOSAxMgo=

4
1 3
2 6
8 10
9 12