import sys

import math

def IL(): return list(map(int,sys.stdin.readline().rstrip().split()))



def Main():

    a,b,n = IL()

    x = min(b-1,n)

    print((math.floor(a*x/b)-a*math.floor(x/b)))

    return



if __name__=='__main__':

    Main()
import sys

import math

def IL(): return list(map(int,sys.stdin.readline().rstrip().split()))

 

def Main():

    a,b,n = IL()

    x = min(b-1,n)

    print((a*x//b))

    return

 

if __name__=='__main__':

    Main()
import sys
import math


def IL():
    return list(map(int, sys.stdin.readline().rstrip().split()))


def Main():
    a, b, n = IL()
    x = min(b - 1, n)
    print((math.floor(a * x / b) - a * math.floor(x / b)))
    return


if __name__ == "__main__":
    Main()

import sys
import math


def IL():
    return list(map(int, sys.stdin.readline().rstrip().split()))


def Main():
    a, b, n = IL()
    x = min(b - 1, n)
    print((a * x // b))
    return


if __name__ == "__main__":
    Main()

-    print((math.floor(a * x / b) - a * math.floor(x / b))) +    print((a * x // b))