#include<bits/stdc++.h>
//#include<ext/pb_ds/assoc_container.hpp>
//#include<ext/pb_ds/tree_policy.hpp>
//
//    #pragma GCC optimize("unroll-loops")
//    #pragma GCC optimize("Ofast")
//    #pragma GCC optimize("-O3")
//    #pragma GCC optimize("no-stack-protector")
//    #pragma GCC optimize("fast-math")

#define fi first
#define f first
#define se second
#define s second
#define vi_a vector<int>a;
#define p_b push_back
////////////////////////////////???????????????CHECK THIS OUT???????????????//////////////////////////////
#define ll long long
////////////////////////////////???????????????CHECK THIS OUT???????????????//////////////////////////////
#define ld long double
#define pll pair<ll,ll>
#define pii pair<int,int>
#define m_p make_pair
#define fast_io cin.tie(0);cout.tie(0);ios_base::sync_with_stdio(0);
#define all(x) x.begin(),x.end()
#define getfiles    ifstream cin("input.txt");ofstream cout("output.txt");
#define pw(x) (1ll << x)
#define sz(x) (ll)x.size()
#define endl "\n"
#define rall(x) x.rbegin(),x.rend()
#define len(a) (ll)a.size()
#define rep(x,l,r) for(ll x=l;x<r;x++)
//#define for(int i=0;i<n;i++) for(ll i=0;i<n;i++)
using namespace std;
//using namespace __gnu_pbds;
ld eps = (ld)1 / 1e6;
ll inf = 1e18, mod2 = 998244353, mod1 = 1e9 + 7;
ll sqr(ll a) { return a * a; }
ll qb(ll a) { return a * a * a; }
ll gcd(ll a, ll b) { return !a ? b : gcd(b % a, a); }
ll binpow(ll a, ll b, ll mod) { return b ? (b % 2 ? (a * (sqr(binpow(a, b / 2, mod)) % mod)) % mod : sqr(binpow(a, b / 2, mod)) % mod) : 1; }
ll binmult(ll a, ll b, ll mod) { return b ? (b % 2 ? (2 * binmult(a, b / 2, mod) + a) % mod : (2 * binmult(a, b / 2, mod)) % mod) : 0; }
/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
//const ll to[5]={0,4,6,7,9};
//const ll N=2*1e5+1;
const ll R=1e4;
//const ll to[7]={1,2,3,1,3,2,1};
const ll tx[4]={0,0,-1,1};
const ll ty[4]={-1,1,0,0};
const char rev_to[4]={'E','W','N','S'};
const ll N=2*1e5+4;
ll n;
vector<ll>b,c,d,e;
ll mx=0;
ll m;
void brute(vector<ll>&a,ll indx,ll prev){
    if(indx==n){
        ll ans=0;
        for(ll i=0;i<sz(b);i++){
            if(a[c[i]]-a[b[i]]==d[i]){
                ans+=e[i];
            }
        }
        mx=max(mx,ans);
    }
    else{
        for(ll i=prev;i<=m;i++){
            a[indx]=i;
            brute(a,indx+1,i);
        }
    }
}
ll brute(ll a,ll b,ll n){
    ll mx=-inf;
    ll mx2=-inf;
    bool ok1=1;
    ll pos;
    for(ll i=0;i<=n;i++){
         if(mx<(a*i/b)-a*(i/b)) pos=i;
        mx=max(mx,(a*i/b)-a*(i/b));
      //   if(mx)
       // cout<<(a*i/b)-a*(i/b)<<" ";
    }
    cout<<pos<<endl;
    return mx;
}
ll solve(ll a,ll b,ll n){
    if(n>=b){
        return (a*(b-1)/b)-a*((b-1)/b);
    }
    else{
         return (a*(n)/b)-a*((n)/b);
    }
}
void check(){
    auto bd=bind(uniform_int_distribution<ll>(1,1000),mt19937(time(0)));
    while(1){
        ll a=bd(),b=bd(),n=bd();
        //ll a=246 ,b=247,n=269;
        cout<<"Testing..."<<a<<" "<<b<<" "<<n<<endl;
        ll ans1=brute(a,b,n),ans2=solve(a,b,n);
        cout<<ans1<<" "<<ans2<<endl;
        if(ans1!=ans2){
            return ;
        }
    }
}
signed main(){
    fast_io;
    ll a,b,n;
    cin>>a>>b>>n;
    cout<<solve(a,b,n);
//    check();
    return 0;
}
/*
    n*(m+1)/2*m;
    10321 300 10031//b-1
    300 1003 100 //n
    a>b -  b-1
    a<=b && n<b - n
    a<=b && n>b
    если WA , то чекер говно, поэтому почекай l8 строчку

*/


Measured memory_bytes: 3696