#include <bits/stdc++.h>

using namespace std;

#define         int              long long int
#define         ff               first
#define         ss               second
#define         mp               make_pair
#define         pb               push_back
#define         pf               push_front
#define         vi               vector<int>
#define         pii              pair<int,int>
#define         qi               queue<int>
#define         mem(a,b)         memset(a,b,sizeof(a))
#define         print(a)         cout << a << '\n'
#define         print2(a)        cout << a << ' '
#define         sorted(arr)      sort(arr.begin(),arr.end())
#define         gcd(a,b)         gcd((a),(b))
#define         lcm(a,b)         ((a)*(b))/gcd((a),(b))
#define         all(v)           v.begin(),v.end()
#define         read(a)          scanf("%d", &a)
#define         f(a,n)           for(int i = a ; i < n ; i++)
#define         in(a , n)        for(int i = 0 ; i < n ; i ++) cin >> a[i];
#define         in2(n,m,arr)     for(int i = 0 ; i < n ; i++){ for(int j = 0; j < m ; j++) cin >> arr[i][j]; }
#define         debug(a)         cerr<<a<<" ";
#define         debug1(a)        cerr<<a<<'\n'
#define         fastio           ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
 

int mod = 1e9 + 7;
const int inf = (int)1e18 + 2;
const int N = 2000020 ;

int power(int x , int y) {
    int res = 1;
    while (y > 0) {
        if (y & 1)
            res = (res * x) ;
        y = y >> 1;
        x = (x * x)  ;
    }
    return res ;
}
void solve(int z) {
    int a , b , n;
    cin >> a >> b >> n;
    if(b == 1) {
        cout << 0 << '\n';
    }
    else {
        int ans = 0;
        if(b % n == 0) {
            ans = ((a * (n - 1)) / b) - (a * ( (n - 1) / b));
            cout << ans;
        }
        else {
            int ans2 = 0 , temp = n / b;
            temp = temp * b;
            temp --;
            ans = ((a * (n)) / b) - (a * ( (n) / b));
            ans2 = ((a * (temp)) / b) - (a * ( (temp) / b));
            cout << max(ans , ans2);
        }
    }
}
/*
 */
int32_t main()
{
    fastio
    int te = 1;
    //cin >> te ;
    int x = 1;
    while(te --) {
        solve(x);
        x ++;
    }
    return 0;
}
 

/* ---------------------------------------------------------------------------------------------------------------------



#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
typedef tree<int, nuint_type, less<int>, rb_tree_tag , tree_order_statistics_node_update> Set;

 
vector<int> ar ;

int get(int x) {
    if (x == ar[x])
        return x;
    return ar[x] = get(ar[x]);
}
void merge(int a ,int b) {
    a = get(a);
    b = get(b);
    if (a == b) {
        return ;
    }
    ar[b] = ar[a];
 }

int sev[100006];
vector<int> pri;
void seive() {
    for(int i = 2 ; i < 100006 ; i ++) {
        if (!sev[i]) {
            for(int j = i ; j < 100006 ; j += i) {
                if(!sev[j])
                    sev[j] = i;
            }
        }
        if(sev[i] == i)
            pri.pb(i);
    }
}
 
 int totient(int n) {
     int result = n;
     for(int i = 2 ; i * i <= n ; i ++){
         if(n % i == 0){
             while(n % i == 0)
                 n /= i;
             result -= result / i;
         }
     }
     if(n > 1)
         result -= result / n;
     return result;
 }
 
 
 int fen[N];
 void add(int idx , int val){
     idx ++;
     while(idx <= N){
         fen[idx] += val;
         idx += (idx & (-idx));
     }
 }
 int query(int idx){
     idx ++;
     int sum = 0;
     while(idx > 0){
         sum += fen[idx];
         idx -= (idx & (-idx));
     }
     return sum;
 }
 
---------------------------------------------------------------------------------------------------------------------*/


Measured memory_bytes: 3652