/* D - Floor Function */

#include <stdio.h>

int main(void){
  long int A, B, N, max = -1, i;
  scanf("%ld %ld %ld", &A, &B, &N);
  for(i = 0; i <= N; i++){
    if(A * i / B - A * (i / B) > max){
      max = A * i / B - A * (i / B);
    }
  }
  printf("%ld\n", max);
}
