'use strict';

const inputs = require('fs').readFileSync('/dev/stdin', 'utf8').split('\n');
const input = inputs[0].split(' ').map(v => parseInt(v, 10));

let result = 0;
for (let i = 1 ; i <= input[2] ; ++i) {
  const tmp = Math.floor(input[0] * i / input[1]) - input[0] * Math.floor(i / input[1]);
  result = Math.max(result, tmp);
}

console.log(result);