#!/usr/bin/env python3
from typing import List

class Solution:
    def __init__(self) -> None:
        self.lines: List[str] = []
        self.left_array: List[int] = []
        self.right_array: List[int] = []
        self.difference_array: List[int] = []
        self.result: int = 0

    def read(self) -> None:
        with open("input") as f:
            self.lines = f.readlines()

    def clean(self) -> None:
        for i in range(len(self.lines)):
            self.lines[i] = self.lines[i].strip()

    def split_lines(self) -> None:
        for line in self.lines:
            elements: List[str] = line.split()
            clean_element: int = int(elements[0])
            self.left_array.append(clean_element)
            clean_element: int = int(elements[1])
            self.right_array.append(clean_element)

    def calculate_occurences(self) -> None:
        for element in self.left_array:
            tmp: int = 0
            for i in range(len(self.right_array)):
                if element == self.right_array[i]:
                    tmp += 1
            self.difference_array.append(element * tmp)

    def calculate_total_similary(self) -> int:
        for i in range(len(self.difference_array)):
            self.result += self.difference_array[i]
        return self.result



def main() -> None:
    solver: Solution = Solution()
    solver.read()
    solver.clean()
    solver.split_lines()
    solver.calculate_occurences()
    solution: int = solver.calculate_total_similary()
    print(solution)

if __name__ == "__main__":
    main()