#include<stdio.h>
#include<stdlib.h>
#include<string.h>

#define ll long long

int main(){
  ll a, b, n, max=0,i;
  scanf("%lld %lld %lld", &a, &b, &n);
  for(i= 1; i<= n; i++){
    ll tmp = a*i/b - a*(i/b);
    max = max>tmp ? max : tmp;
    // printf("%lld\n", max);
  }
  
  printf("%lld\n", max);
  return 0;
}