function Main(input){
  input = input.split(' ').map(x=>BigInt(x));
  var a = input[0];
  var b = input[1];
  var n = input[2];
  if (b==1){
    var max = a*n 
  }else if (n<b){
    var max = a*n/b - a*(n/b);
  }else{
    var border = (n+1n)/b;
    var t = 1n;
    var max = 0n;
    for (let t = 1n;t<=border;t++){
      var now = a*(b*t-1n)/b - a*((b*t-1n)/b);
      if (now > max){
        max = now;
      }
    }
  }
  console.log(max.toString())
}
  

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