const Main = (input) => {
  const tmp = input.trim().split(' ').map(n => parseInt(n))
  const A = tmp[0]
  const B = tmp[1]
  const N = tmp[2]

  let x = Math.min(B, N)

  if (B === N) x -= 1

  const result = Math.floor((A * x / B))

  console.log(result)
  return result
}

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