#include #define EPS 1e-9 #define INF 1070000000LL #define MOD 1000000007LL #define fir first #define foreach(it,X) for(auto it=(X).begin();it!=(X).end();it++) #define numa(x,a) for(auto x: a) #define ite iterator #define mp make_pair #define rep(i,n) rep2(i,0,n) #define rep2(i,m,n) for(int i=m;i<(n);i++) #define pb push_back #define pf push_front #define sec second #define sz(x) ((int)(x).size()) #define ALL( c ) (c).begin(), (c).end() #define gcd(a,b) __gcd(a,b) #define mem(x,n) memset(x,n,sizeof(x)) #define endl "\n" using namespace std; template void deploy(std::ostream &os, const TUPLE &tuple){} template void deploy(std::ostream &os, const TUPLE &t){ os << (POS == 0 ? "" : ", ") << get(t); deploy(os, t); } template std::ostream& operator<<(std::ostream &os, std::pair &p){ os << "(" << p.first <<", " << p.second <<")";return os; } template std::ostream& operator<<(std::ostream &os, std::vector &v){ int remain = v.size(); os << "{"; for(auto e: v) os << e << (--remain == 0 ? "}" : ", "); return os; } template std::ostream& operator<<(std::ostream &os, std::set &v){ int remain = v.size(); os << "{"; for(auto e: v) os << e << (--remain == 0 ? "}" : ", "); return os; } template std::ostream& operator<<(std::ostream &os, std::map &mp){ int remain = mp.size(); os << "{"; for(auto e: mp) os << "(" << e.first << " -> " << e.second << ")" << (--remain == 0 ? "}" : ", "); return os; } #define DEBUG1(var0) { std::cerr << (#var0) << "=" << (var0) << endl; } #define DEBUG2(var0, var1) { std::cerr << (#var0) << "=" << (var0) << ", ";DEBUG1(var1); } #define DEBUG3(var0, var1, var2) { std::cerr << (#var0) << "=" << (var0) << ", ";DEBUG2(var1,var2); } #define DEBUG4(var0, var1, var2, var3) { std::cerr << (#var0) << "=" << (var0) << ", ";DEBUG3(var1,var2,var3); } using ll = long long; ll d; ll calc(ll x, ll y){ return floor((x - y) / d) + 1; } int main() { cin.tie(0); ios_base::sync_with_stdio(0); ll nums[3]; cin >> d; rep(i,3){ cin >> nums[i]; } if (d == 0) { cout << -1 << endl; return 0; } if (nums[0] > nums[1]) { swap(nums[0],nums[1]); } if (nums[0] == nums[2]) { if (nums[0] != nums[1]) { cout << 1 << endl; return 0; } cout << 2 << endl; return 0; } if (nums[0] == nums[1]) { if (nums[0] - d >= 0 || nums[1] + d != nums[2]) { cout << 1 << endl; return 0; } cout << 2 << endl; return 0; } if (nums[2] == nums[1]) { cout << 1 << endl; return 0; } if (nums[0] < nums[1] && nums[1] < nums[2]) { ll a = floor(nums[2] - nums[1] / d) + 1; ll minh = nums[1] % d; if (nums[0] <= minh) { if (nums[0] + d == nums[2]) { a = min(a,2LL); }else if (nums[0] + d > nums[2]){ a = min(a,1LL); }else{ if (nums[0] + d > nums[1]) { a = min(a,1LL); }else if (nums[0] + d < nums[1]){ a = min(a, (ll) floor((nums[1] - nums[0] + d) / d) + 2); }else{ a = min(a,2LL); } } }else{ a = min(a, (ll) floor(nums[1] - nums[0] / d) + 1); } cout << a << endl; }else{ cout << 0 << endl; } return 0; }