#include <stdio.h>

int main(void)
{
  long long int a, b, n, i, tmp=1, ans=0, ans_tmp;

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

  for (i = 0; i <= n; i++) {
    if (b*tmp-1 <= n) i = b*tmp-1;
    ans_tmp = (long long int)(a*i/b) - a*(long long int)(i/b);
    if (ans < ans_tmp)
      ans = ans_tmp;
    tmp++;
  }

  printf("%lld", ans);

  return 0;
}
