#!/usr/bin/env python3

import itertools


def divceil(a, b):
    return (a + b - 1) // b


def compute_min_amount(a, b, t):
    def amount(x):
        return b * x + a * divceil((t - b * x), a)
    xs = itertools.takewhile(lambda x: b * (x - 1) < t, range(a + 1))
    return min(amount(x) for x in xs)


def main():
    a, b, t = map(int, input().split())
    print(compute_min_amount(a, b, t))


if __name__ == '__main__':
    main()