#include<stdio.h>
#include<stdlib.h>
#include<math.h>
int main(){
  int unused __attribute__((unused));
  long long A, B, N, x;
  unused = scanf("%lld %lld %lld", &A, &B, &N);

  x = fmin(B-1, N);
  printf("%lld", A*x/B - A*(x/B));
  return 0;
}