Growth in 2 Dimensions

Each operation adds 1 to the rectangle spanning from the bottom-left corner to (r,c); find the number of cells that end up holding the maximum value.

输入格式

The first line contains q (1≤q≤100000), followed by q lines, each with positive integers r and c (≤10^9).

输出格式

Output the number of cells that reach the maximum value (use a 64-bit integer).

样例 1

输入：

3
1 4
2 3
4 1

输出：

1

样例说明

Derive a linear-scan/dynamic-programming solution directly from the problem rules; the examples have been checked case by case against an independently built oracle.