#include <stdio.h>
#include <math.h>

int main(void)
{
  long int i, a, b, n, max = 0, fa, fb;
  
  scanf("%ld %ld %ld", &a, &b, &n);
  
  if( n > b ){
      n = b-1;
  }
  
  for( i = n; i <= n; i++ ){
      fa = a*i/b;
      fb = i/b;
      if( max < fa - (a*fb) ){
          max = fa - (a*fb);
      }
  }
  

  printf("%ld\n", max);
  return 0;
}