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

int main(){
  long long a,b,n;
  long long x;
  long long max = -999999;
  long long ans;
  long long t1,t2;

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

  t1 = a*n/b - a*(n/b);
  t2 = a*(a/b)/b - a*(a/(b*b));

  if(t1 < t2) ans = t2;

  else ans = t1;

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

  return 0;
}
