#include <iostream>
#include <iomanip>
#include <string>
#include <algorithm>
using namespace std;
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define rep2(i,s,n) for(int i = (s);i<(int)(n);i++)

int main(){
    int a , b , n;
    cin >> a >> b >> n;
    long long k[n];
    long long max = 0;
    rep2(i,1,n+1){
        int s = (a*i)/b;
        int t = (i/b);
        k[i] = s - a*t;
        if(max < k[i]){
                max = k[i];
        }
    }
    cout << max << endl;
}
