function MainD(input){
    const [A, B, N] = input.split(' ');
    const answer1 = Math.floor((A * N)/B) - A *  Math.floor(N/B);
    const answer2 = Math.floor((A * (N-1))/B) - A *  Math.floor((N-1)/B);
    console.log(answer1 > answer2 ? answer1 : answer2);
}
MainD(require("fs").readFileSync("/dev/stdin", "utf8").trim());
