#pragma region Macros
#include <bits/stdc++.h>
using namespace std;
// iteration helper
#define FOR(i, l, r) for (int i = (l); i < (r); ++i)
#define REP(i, n) FOR(i, 0, n)
#define RFOR(i, l, r) for (int i = (r)-1; i >= (l); --i)
#define RREP(i, n) RFOR(i, 0, n)
#define EACH(i, c)                                                             \
    for (typeof((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define EXIST(s, e) ((s).find(e) != (s).end())
#define PB push_back

// typedefs
#define ll long long
#define vi vector<int>
#define vi2 vector<vi>
// input
#define ci(x)                                                                  \
    int x;                                                                     \
    cin >> x
#define cs(x)                                                                  \
    string x;                                                                  \
    cin >> x
#define cd(x)                                                                  \
    double x;                                                                  \
    cin >> x
#define cvi(x, n)                                                              \
    vi x(n);                                                                   \
    REP(i, n) { cin >> x[i]; }
// const input
#define cci(x)                                                                 \
    const int x = []() {                                                       \
        int t;                                                                 \
        cin >> t;                                                              \
        return t;                                                              \
    }()
#define ccs(x)                                                                 \
    const string x = []() {                                                    \
        string t;                                                              \
        cin >> t;                                                              \
        return t;                                                              \
    }()
#define ccd(x)                                                                 \
    const double x = []() {                                                    \
        double t;                                                              \
        cin >> t;                                                              \
        return t;                                                              \
    }()
// output
#define pr(x) cout << x << endl
#define prvec(v) REP(i, v.size()) pr(v[i])
#define ppr(x) cout << x
#define lf() cout << endl
// debug methods
// usage: debug(x,y);
#define CHOOSE(a) CHOOSE2 a
#define CHOOSE2(a0, a1, a2, a3, a4, x, ...) x
#define debug_1(x1) cout << #x1 << ": " << x1 << endl
#define debug_2(x1, x2)                                                        \
    cout << #x1 << ": " << x1 << ", " #x2 << ": " << x2 << endl
#define debug_3(x1, x2, x3)                                                    \
    cout << #x1 << ": " << x1 << ", " #x2 << ": " << x2 << ", " #x3 << ": "    \
         << x3 << endl
#define debug_4(x1, x2, x3, x4)                                                \
    cout << #x1 << ": " << x1 << ", " #x2 << ": " << x2 << ", " #x3 << ": "    \
         << x3 << ", " #x4 << ": " << x4 << endl
#define debug_5(x1, x2, x3, x4, x5)                                            \
    cout << #x1 << ": " << x1 << ", " #x2 << ": " << x2 << ", " #x3 << ": "    \
         << x3 << ", " #x4 << ": " << x4 << ", " #x5 << ": " << x5 << endl
#ifdef _DEBUG
#define debug(...)                                                             \
    CHOOSE((__VA_ARGS__, debug_5, debug_4, debug_3, debug_2, debug_1, ~))      \
    (__VA_ARGS__)
#else
#define debug(...)
#endif
// const number
const double PI = acos(-1.0);
const double EPS = 1e-10;

int powint(int a, int x) {
    int res = 1;
    REP(i, x) { res = res * a; }
    return res;
}
#pragma endregion
#define int long long
signed main() {
#ifdef _DEBUG
    try {
#endif
        // main program ---------------------------------------------
        cci(A);
        cci(B);
        cci(N);
        int q = min(N, B - 1);
        int ans = (int)((A * q) / B);
        pr(ans);
// end main program -----------------------------------------
#ifdef _DEBUG
    } catch (std::out_of_range &ex) {
        pr("out of range");
    }
#endif
    return 0;
}


Measured memory_bytes: 3632