"use strict";

const main = arg => {
    const input = arg.trim().split("\n");

    const a = parseInt(input[0].split(" ")[0]);
    const b = parseInt(input[0].split(" ")[1]);
    const n = parseInt(input[0].split(" ")[2]);

    const helper = function(x){
        return Math.trunc(a*x/b) - a*Math.trunc(x/b)
    }
    let max = Number.NEGATIVE_INFINITY
    for(let x = 0; x<=n;x++){
        max = Math.max(max, helper(x))
    }
    console.log(max)
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));  