let arr=readLine()!.split{$0==" "}.map{Int(String($0))!}
var a=arr[0]
var b=arr[1]
var c=arr[2]
var maxN:Int = 0
for i in 0..<c+1 {
  let j = floor(Float(a*i)/Float(b))-Float(a)*floor(Float(i)/Float(b))
    maxN = max(maxN, Int(j))
}
print(maxN)