#include <iostream>
#include <iomanip>
#include <cassert>
#include <cstdint>
#include <vector>
#include <string>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <array>
#include <deque>
#include <stack>
#include <queue>
#include <algorithm>
#include <functional>
#include <utility>
#include <cmath>
#include <numeric>
#include <sstream>

using namespace std;

#ifdef _DEBUG
#define DUMP(x) std::cerr << (#x) << " = " << (x) << "\n"
#else
#define DUMP(x)
#endif
#define REP(i, a, b) for (int i = (int)(a); i < (int)(b); ++i)
#define EREP(i, a, b) for (int i = (int)(a); i <= (int)(b); ++i)
#define RREP(i, a, b) for (int i = (int)(a)-1; i >= (int)(b); --i)
#define rep(i, n) REP(i, 0, n)
#define erep(i, n) EREP(i, 0, n)
#define rrep(i, n) RREP(i, n, 0)
#define ALL(r) (r).begin(), (r).end()
#define pb push_back
#define eb emplace_back
#define fi first
#define se second

template <typename T>
ostream &operator<<(ostream &os, vector<T> &v)
{
    os << "{";
    rep(i, v.size()) os << v[i] << (i == (int)v.size() - 1 ? "" : ", ");
    os << "}";
    return os;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, pair<T, U> &p) { return (os << "(" << p.first << ", " << p.second << ")"); }
template <typename T, typename U>
ostream &operator<<(ostream &os, map<T, U> &m)
{
    bool first = true;
    os << "{";
    for (const auto &e : m)
    {
        if (!first)
            os << ", ";
        os << "{" << e.first << ": " << e.second << "}";
        first = false;
    }
    os << "}";
    return os;
}
template <typename T>
ostream &operator<<(ostream &os, set<T> &s)
{
    os << "{";
    bool first = true;
    for (const auto &e : s)
    {
        if (!first)
            os << ", ";
        os << e;
        first = false;
    }
    os << "}";
    return os;
}
template <typename T>
T dup(T x, T y) { return (x + y - 1) / y; };
template <typename A, size_t N, typename T>
inline void arrayFill(A (&array)[N], const T &val) { std::fill((T *)array, (T *)(array + N), val); }
template <class T>
inline bool chmax(T &a, T b)
{
    if (a < b)
    {
        a = b;
        return true;
    }
    return false;
}
template <class T>
inline bool chmin(T &a, T b)
{
    if (a > b)
    {
        a = b;
        return true;
    }
    return false;
}
struct in
{
    const size_t n = 0;
    in() = default;
    in(size_t n) : n(n){};
    template <typename T>
    operator T()
    {
        T ret;
        cin >> ret;
        return ret;
    }
    template <typename T>
    operator vector<T>()
    {
        assert(n != 0);
        vector<T> ret(n);
        for (T &x : ret)
        {
            T tmp = in();
            x = tmp;
        }
        return ret;
    }
    template <typename T, typename U>
    operator pair<T, U>()
    {
        pair<T, U> ret;
        ret.first = in();
        ret.second = in();
        return ret;
    }
};
template <typename T>
inline void out(T x) { std::cout << x << '\n'; };

using ll = int64_t;
using vint = vector<int32_t>;
using vvint = vector<vint>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vstr = vector<string>;
using pint = pair<int32_t, int32_t>;
using vpint = vector<pint>;
using pll = pair<ll, ll>;
using vpll = vector<pll>;
using setint = set<int32_t>;
using qint = queue<int32_t>;
using qpint = queue<pint>;

constexpr std::int32_t INF = 1001001001;
constexpr std::int64_t LINF = 1001001001001001001;

constexpr double GRAITO = 1.6180339887498948482045868343656;
// 黄金分割探索
// f(x)が区間[lb, ub]で下に凸ならば、その極値を取るxを返す
// 反復時に値が使い回せるので、fの計算が1回で済む
// f: 凸関数
// lb: 下限
// ub: 上限
// k: 反復回数
double goldenSectionSearch(function<double(double)> f, double lb, double ub, int k)
{
    double x1 = (ub - lb) / (GRAITO + 1) + lb; // 内分点(1:GRAITO)
    double x2 = (ub - lb) / GRAITO + lb;       // 内分点(GRAITO:1)
    double f1 = f(x1), f2 = f(x2);

    rep(i, k)
    {
        if (f1 < f2)
        {
            // 右側の区間を除外する
            ub = x2;
            x2 = x1; // 内分点（左）を次の内分点（右）に採用する
            f2 = f1;
            x1 = (ub - lb) / (GRAITO + 1) + lb; // 次の内分点（左）を計算する
            f1 = f(x1);
        }
        else
        {
            // 左側の区間を除外する
            lb = x1;
            x1 = x2; // 内分点（右）を次の内分点（左）に採用する
            f1 = f2;
            x2 = (ub - lb) / GRAITO + lb; // 次の内分点（右）を計算する
            f2 = f(x2);
        }
    }
    return (lb + ub) / 2;
}

void Main()
{
    ll a = in(), b = in(), n = in();
    auto f = [=](ll x) { return -(a * x / b - a * (x / b)); };

    double d = goldenSectionSearch(f, 0, n, 300);
    DUMP(d);
    ll l = max((ll)d - 10, (ll)0);
    ll h = min((ll)d + 10, (ll)n);
    ll ans = -LINF;
    for (ll i = l; i <= h; ++i)
    {
        ans = max(-f(i), ans);
    }
    out(ans);
}

signed main()
{
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << std::fixed << std::setprecision(15);
    Main();
    return 0;
}


Measured memory_bytes: 3656