#pragma comment(linker, "/STACK:65777216")
#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <ctime>
#include <cstdio>
#include <algorithm>
#include <cmath>
#include <vector>
#include <set>
#include <stack>
#include <map>
#include <queue>
#include <string>
#include <memory.h>
#include <iterator>
#define mem(A,X) memset(A,X,sizeof(A))
#define memo(A) memset(A,0,sizeof(A))
#define forn(I,B) for (int I=1;I<=(B);I++)
#define forg(H,V) for (int H=first[V];h;h=next[H])
#define rep(I,B) for (int I=0;I<(B);I++)
#define labs(X) (((X)>0)?(X):(-(X)))
#define ropen(X) freopen(X,"r",stdin)
#define wopen(X) freopen(X,"w",stdout)
#define pb push_back
#define mp make_pair
#define all(X) (X).begin(),(X).end()
#define sqr(X) ((X)*(X))

using namespace std;

typedef pair <int,int> pii;
typedef pair <long long,long long> pll;
typedef double ld;
typedef long long ll;
typedef vector<int> vi;
const int N=111111;
const int INF=111111111;
const double eps=1e-9;
const double pi=3.14159265358979;

int ys[N];

int main(){
    int a,x,y;
    cin>>a>>x>>y;
    if (y%a==0 || x>=a || x<=-a){
        cout<<-1;
        return 0;
    }
    ys[1]=a;ys[2]=a+a;
    ys[3]=ys[4]=a+a+a;
    for (int i=1;;i++){
        if (i>=5){
            if (i%3==2) ys[i]=ys[i-1]+a;
            if (i%3==1) ys[i]=ys[i-2]+a;
            if (i%3==0) ys[i]=ys[i-1]+a;
        }
        if (ys[i]>y){
            if (i%3==2 || i==1 || i==2){
                if (2*x>=a || 2*x<=-a){
                    cout<<-1;
                    return 0;
                } else {
                    cout<<i;
                    return 0;
                }
            } else {
                if (x==0){
                    cout<<-1;
                    return 0;
                } else {
                    if (x<0 && x>-a){
                        cout<<i;
                        return 0;
                    } else {
                        cout<<i+1;
                        return 0;
                    }
                }
            }
        }
    }
}