#include <stdio.h>
#include <string.h>
#define MIN(x, y) (((x) > (y)) ? (y) : (x))
#define ABS(x) ((x) >= 0 ? (x) : (-(x)))


int main()
{
  long long a, b, n;
  scanf("%lld %lld %lld", &a, &b, &n);
  if (n >= b) {
    printf("%lld", (b - 1) * a / b);
  } else {
    printf("%lld", n * a / b);
  }
  return 0;
}