import sequtils,strutils
var
    A, B, T : int64
(A, B, T) = stdin.readline.split.map(parseBiggestInt)
var
    b = (T + B - 1) div B
    ans = b * B

while b > 0 and T < ans:
    b -= 1
    var a = (T - b * B - 1 + A) div A
    ans = min(ans, a * A + b * B)

echo ans