function main(input) {
  let a,b,n;
  [a, b, n] = input[0].trim().split(" ").map(i => parseInt(i));

  let max = -100000000;
  for(let i=1;i<=n;i++){
    const s = Math.floor(a*i/b) - a*Math.floor(i/b);
    if(max<s){
      max=s;
    }
  }
  console.log(max);
}
main(require('fs').readFileSync('/dev/stdin', 'utf8').trim().split("\n"));