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

#define ll long long

int main(){
  ll a, b, n, ans;
  scanf("%lld %lld %lld", &a, &b, &n);

  if(b-1>=n){
    ans = a*n/b - a*(n/b);
  }else{
    ans = a*(b-1)/b - a*((b-1)/b);
  }
  printf("%lld\n",ans);
  return 0;
}