function Main(input){
  input = input.split(' ').map(x=>BigInt(x));
  var a = input[0];
  var b = input[1];
  var n = input[2];
  var max = 0n;
  for (let x=1n;x<=n;x++){
    var now = a*x/b - x/b*a;
    if (now > max){
      max = now;
    }
  }
  console.log(max.toString())
}
  

Main(require("fs").readFileSync("/dev/stdin", "utf8"));