const Main = input => {
  const [ A, B, N ] = input.split(' ').map(e => Number(e));
  
  let max = 0;
  for(let x=1; x<=N; x++) {
    //console.log(x, Math.floor(A*x/B), Math.floor(x/B));
    const result = Math.floor(A*x/B) - A*Math.floor(x/B);
    if(result > max) max = result;
  }

  console.log(max);
};

Main(require('fs').readFileSync('/dev/stdin', 'utf8').trim());
//Main(`5 7 4`);
//Main(`11 10 9`)
