Problem:
Score : 400 points

Problem Statement

Given are integers A, B, and N.

Find the maximum possible value of floor(Ax/B) - A × floor(x/B) for a non-negative integer x not greater than N.

Here floor(t) denotes the greatest integer not greater than the real number t.

Constraints

1 ≤ A ≤ 10^{6}

1 ≤ B ≤ 10^{12}

1 ≤ N ≤ 10^{12}

All values in input are integers.

Input

Input is given from Standard Input in the following format:

A B N

Output

Print the maximum possible value of floor(Ax/B) - A × floor(x/B) for a non-negative integer x not greater than N, as an integer.

Sample Input 1

5 7 4

Sample Output 1

2

When x=3, floor(Ax/B)-A×floor(x/B) = floor(15/7) - 5×floor(3/7) = 2. This is the maximum value possible.

Sample Input 2

11 10 9

Sample Output 2

9

Solution in C++ (GCC 9.2.1) (judge verdict: Accepted)

#include <bits/stdc++.h>

#define reb(i,b,n) for(int i=(int)(b); i<(int)(n); i++)
#define rep(i,n) reb(i,0,n)
#define rreb(i,b,n) for(int i = b-1; i >= n; i--)
#define rrep(i,n) reb(i,n,0)
#define each(it,v) for(__typeof((v).begin()) it=(v).begin();it!=(v).end();it++)
#define reach(it,v) for(__typeof((v).rbegin()) it=(v).rbegin();it!=(v).rend();it++)
#define vall(x) (x).begin(), (x).end()
#define rvall(x) (x).rbegin(), (x).rend()
#define vsort(v) sort(vall(v))
#define rvsort(v) sort(rvall(v))
#define len(array) (sizeof (array) / sizeof *(array))
#define aall(x) x, x+len(x)
#define asort(x) sort(aall(x))
#define rasort(a, type) sort(aall(a), greater<type>())
#define afill(a, v) fill(aall(a), v)
#define afill2(a, v, type) fill((type *)a, (type *)(a + len(a)), v)
#define sz(x) (int)(x).size()
#define mp(a, b) make_pair(a, b)
#define fi first
#define se second
#define pb push_back
#define _USE_MATH_DEFINES
#define priArr(table, n) rep(i,n){cout<<table[i]<<' ';}cout<<'\n';
#define priAr2(table,W,H) rep(y,H){rep(x,W)cout<<table[y][x]<<' ';cout<<'\n';}
#define dbg(x) cerr<<__LINE__<<": "<<#x<<" = ["<<(x)<<"]"<<endl;

using namespace std;
using std::stringstream;

inline int toInt(string s) {int v; istringstream sin(s);sin>>v;return v;}
template<class T> inline std::string toString(T x) {ostringstream sout;sout<<x;return sout.str();}
template<class F, class T> inline void convert(const F &f, T &t){stringstream ss;ss<<f;ss>>t;}
template<class T> inline T sqr(T x) {return x*x;}

typedef long long ll; typedef unsigned long long ull;
typedef pair <int, int> P; typedef pair <int, P> PP;
typedef vector<int> vi;typedef vector<vi> vvi;typedef vector<string> vs;
typedef vector<ll> vl; typedef vector<P > vP; typedef vector<char> vc;
typedef long double ld;

const static int INF = 0x3f3f3f3f;
const static ll INFL = 0x3f3f3f3f3f3f3f3fLL;
const static double EPS = 1e-9;
const static ll MOD = 1000000007LL;

int dx[] = {1,0,-1,0}, dy[] = {0,1,0,-1};
/* -------------------------------------------------------------------------- */

int main(int argc, char *argv[])
{
    ll A, B, N;
    cin >> A >> B >> N;

    ll x;
    x = ((N < B) ? N : B-1);


    ll ans;
    ll fla, flb;
    fla = ((A * x)/B);
    flb = x/B;

    ans = fla - A * flb;

    cout << ans << endl;;

    return 0;
}