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

typedef long long ll;


int main(){
  ll a,b,n,x;

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

  x = n;

  if(n >= b - 1) x = b - 1;

  printf("%lld\n", a*(x % b)/b);

  return 0;
}
