#include<bits/stdc++.h>
using namespace std;

typedef long long ll;
int main()
{
    ios_base::sync_with_stdio(0);cin.tie(0);
    cout.tie(0);
    ll a,b,n;
    cin>>a>>b>>n;
    ll x=min(n,b-1);
    double ans=(1.0*(a/(1.0*b))*x);
    ll res=ans;
    ll t=(x/b);
    res-=(a*t);
    cout<<res<<endl;
    return 0;
}