Problem:
Score : 100 points

Problem Statement

ButCoder Inc. runs a programming competition site called ButCoder. In this site, a user is given an integer value called rating that represents his/her skill, which changes each time he/she participates in a contest. The initial value of a new user's rating is 0, and a user whose rating reaches K or higher is called Kaiden ("total transmission"). Note that a user's rating may become negative.

Hikuhashi is a new user in ButCoder. It is estimated that, his rating increases by A in each of his odd-numbered contests (first, third, fifth, ...), and decreases by B in each of his even-numbered contests (second, fourth, sixth, ...).

According to this estimate, after how many contests will he become Kaiden for the first time, or will he never become Kaiden?

Constraints

1 ≤ K, A, B ≤ 10^{18}

All input values are integers.

Input

Input is given from Standard Input in the following format:

K A B

Output

If it is estimated that Hikuhashi will never become Kaiden, print -1. Otherwise, print the estimated number of contests before he become Kaiden for the first time.

Sample Input 1

4000 2000 500

Sample Output 1

5

Each time Hikuhashi participates in a contest, his rating is estimated to change as 0 → 2000 → 1500 → 3500 → 3000 → 5000 → … After his fifth contest, his rating will reach 4000 or higher for the first time.

Sample Input 2

4000 500 2000

Sample Output 2

-1

Each time Hikuhashi participates in a contest, his rating is estimated to change as 0 → 500 → -1500 → -1000 → -3000 → -2500 → … He will never become Kaiden.

Sample Input 3

1000000000000000000 2 1

Sample Output 3

1999999999999999997

The input and output values may not fit into 32-bit integers.

Solution in C (GCC 5.4.1) (judge verdict: Runtime Error)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <math.h>
#include <limits.h>
#include <assert.h>
#define FOR(i,a,n) for(i=(a);i<(n);i++)
#define swap(type,a,b) do{type t=a;a=b;b=t;}while(0)
#define MAX(a,b) (((a)>(b))?(a):(b))
#define MIN(a,b) (((a)<(b))?(a):(b))
#define ll long long
#define INF 100000000
#define MOD 1000000007
#define SIZE 100005
#define LOCAL
#ifdef LOCAL
    #define DEBUG(...) printf(" "__VA_ARGS__)
#else
    #define DEBUG(...)
#endif /* LOCAL */
int comp(const void* a,const void* b){
	return *(int*)a-*(int*)b;
}

int main(void)
{
	ll k,a,b,d;
	scanf("%lld%lld%lld",&k,&a,&b);
	if(k<=a) puts("1");
	else{
		k-=a,d=a-b;
		if(d<0) puts("-1");
		else printf("%lld\n",(k+d-1)/d*2LL+1);
	}
	return 0;
}