function Main(input) {
  input = input.split(' ')
  const A = parseInt(input[0])
  const B = parseInt(input[1])
  const N = parseInt(input[2])

  let max = 0;
  for(x = 1; x <= N; x++){
    const temp = Math.floor(A * x / B) - A * Math.floor(x / B);
    if (max < temp) max = temp;
  }

  console.log(max)
}

// Don't edit this line!
Main(require("fs").readFileSync("/dev/stdin", "utf8"));