import sys
import math

# Auto-generated code below aims at helping you parse
# the standard input according to the problem statement.

robbers = int(raw_input())
vaults = int(raw_input())
print >> sys.stderr, robbers, vaults

numbers = 10
vowels = 5

characters = [0] * vaults
digits = [0] * vaults

def process_window(window_length, seconds):
    lowest_seconds = 999999999999999999999999999999999999999999999999999999999
    for i in xrange(window_length):
        if seconds[i] < lowest_seconds:
            lowest_seconds = seconds[i]
    return lowest_seconds

def find_blanks(window_length, seconds):
    index = []
    for i in xrange(window_length):
        if seconds[i] == 0:
            index.append(i)
    return index


for i in xrange(vaults):
    characters[i], digits[i] = [int(j) for j in raw_input().split()]
    print >> sys.stderr, characters[i], digits[i]

# Write an action using print
# To debug: print >> sys.stderr, "Debug messages..."
seconds = []

# compute seconds for each vault
for i in xrange(vaults):
    first_combo = pow(numbers, digits[i])
    num_charcters = characters[i] - digits[i]
    second_combo = pow(vowels, num_charcters)
    seconds.append(first_combo * second_combo)


total_seconds = 0
print >> sys.stderr, seconds
while seconds:
    time_taken = 0
    window_length = 0
    # find windows length
    if robbers < len(seconds):
        window_length = robbers
    else:
        window_length = len(seconds)
    # find time in window
    time_taken = process_window(window_length, seconds)
    total_seconds += time_taken

    ## take time and remove 0 time elements
    for i in xrange(window_length):
        seconds[i] = seconds[i] - time_taken
    items_to_remove = find_blanks(window_length, seconds)

    for item in items_to_remove:
        seconds.pop(item)
    print >> sys.stderr, time_taken, seconds, total_seconds

print total_seconds