#include <stdio.h>

typedef long long ll;

ll floor1(double x) {
  return (ll)x;
}

int main(void) {

  ll a, b, n;
  scanf("%lld %lld %lld", &a, &b, &n);
  ll max = 0;
  for(ll i = 1;i <= n;i++) {
    ll tmp = floor1(a * i / (double)b) - a * floor1(i / (double)b);
    max = tmp > max ? tmp : max;
  }
  printf("%lld\n", max);

  return 0;
}
