#include <stdio.h>
int main() {
  
long long int a, b, n;
scanf("%lld", &a);
scanf("%lld", &b);
scanf("%lld", &n);

long long int x = b - 1;
long long int t = 2;
long long int maxnum = -1;
long long int tmp = 0;

while(x < n){
  x = t * b - 1;
  tmp = a * x / b - x / b * a;
  if (maxnum < tmp){
    maxnum = tmp;
  }
  t++;
}
x = n;
tmp = a * x / b - x / b * a;
if (maxnum < tmp){
  maxnum = tmp;
}

printf("%lld", maxnum);

}