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

int main(void)
{
  long long int a,b,n;
  long long int ans;

  scanf("%lld %lld %lld",&a,&b,&n);

  if(b-1<=n) ans=(long long int)floor((double)a*((double)(b-1)/(double)b));
  else ans=(long long int)floor((double)a*((double)n/(double)b));

  printf("%lld\n",ans);

  return 0;
}