Process Execution Time

Each process runs during the integer closed interval [start[i],end[i]]. Find the number of integer moments at which at least one process is running. The source statement body is truncated; the original example explicitly merges overlapping intervals into [1,6], counting 6, then adds [8,10], counting 3, and the union-length rule is recovered from that explanation.

输入格式

The first line contains n, followed by n lines of start end. Full original bounds: 1≤n≤200000, 1≤start≤end≤10^9.

输出格式

Output one integer, the answer.

样例 1

输入：

3
1 5
2 6
8 10

输出：

9

样例 2

输入：

1
5 5

输出：

1

样例 3

输入：

3
3 8
1 10
10 10

输出：

10

样例说明

The outputs of the three public examples are, in order: 9; 1; 10. These answers were verified by independent enumeration or direct simulation.