Xiaoyang's Smart Shopping

Problem Description

Xiaoyang's class is holding an eco-friendly handcraft exhibition, and the teacher asks Xiaoyang to go to the stationery store to buy $M$ different kinds of stationery (for example: pencils, erasers, rulers, etc.).

The store has $N$ items in total, and each item has a type id (from $1$ to $M$) and a price.

Xiaoyang's budget is limited, so he came up with a clever idea: for each kind of stationery, he only buys the cheapest one (if several items of the same kind share the lowest price, he buys only one of them). Please help Xiaoyang compute how much he needs to spend in total to buy all $M$ kinds of stationery.

Input Format

The first line contains two positive integers $M, N$, the number of kinds of stationery and the total number of items.

The following $N$ lines each contain two positive integers $K_i$ and $P_i$, representing the type id and the price of the $i$-th item. The data guarantees that each kind has at least one item available to buy.

Output Format

Output one line: the total price of the stationery purchased.

Sample Input

2 5
1 1
1 2
1 1
2 3
2 10

Sample Output

4

Sample Explanation

The item list is as follows:

• Item 1: type $1$, price $1$
• Item 2: type $1$, price $2$
• Item 3: type $1$, price $1$
• Item 4: type $2$, price $3$
• Item 5: type $2$, price $10$

Xiaoyang's selection process: for type $1$, there are three items priced $1, 2, 1$, the cheapest of which is $1$; for type $2$, there are two items priced $3, 10$, the cheapest of which is $3$.

Total price: Xiaoyang spends $1 + 3 = 4$ in total for these two kinds of stationery.

Constraints

For all test cases, $1 \leq M \leq N \leq 10^5$, $1 \leq K_i \leq M$, $1 \leq P_i \leq 10^3$.