function Main(input){
	input = input.split(' ');
  	const [a,b,n] = input;
  	
  	const x = Math.min(b-1, n);
  
	const ans = Math.floor(a*x/b) - a * Math.floor(x/b);
  	console.log(ans);
}

// Don't edit this line!
Main(require("fs").readFileSync("/dev/stdin", "utf8"));