#define int unsigned long long

main () {
    int a, b, n, maxscore, x, score;
    scanf("%lld %lld %lld", &a, &b, &n);

    if (n / b > 1) {
        x = (n / b - 1) * b + (b - 1);
        score = (int)(a * x / (double)b) - a * (int)(x / (double)b);
        if (score > maxscore) maxscore = score;
    }

    score = (int)(a * n / (double)b) - a * (int)(n / (double)b);
    if (score > maxscore) maxscore = score;

    printf("%lld\n", maxscore);

    return 0;
}
