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

int main(){
  long long a,b,n;
  long long x = 1;
  long long max = -999999;
  long long ans;

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

  for(x = n;x >= 0;x -= b){
    ans = a*x/b - a*(x/b);

    if(max < ans) max = ans;
  }

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

  return 0;
}
