#include <stdio.h>

#define int64 long long

int64 floor(int64 xx, int64 bb)
{
  return (xx / bb);
}

int main()
{
  int64 aa, bb, nn;
  scanf("%lld %lld %lld", &aa, &bb, &nn);
  int64 tmp, ans = -1;
  for(int64 xx = nn;xx > 0;xx--)
  {
    tmp = floor(aa * xx, bb) - aa * floor(xx, bb);
    if(tmp > ans)
    {
      ans = tmp;
    }
  }
  printf("%lld\n", ans);
  return 0;
}