#include<bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp> // #include<ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp> //#include<ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds; //using namespace __gnu_pbds;
#define pb push_back
#define ins insert
#define var auto
#define F first
#define S second
#define mp make_pair
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
template <class T> using oset = tree<T, null_type, less<T>, rb_tree_tag,tree_order_statistics_node_update>;
const int Max = 1e6 + 10;
const int LOG = 30;
const int Mod = 998244353;
const int SQ = 3000;
const int INF = 1e9 + 10;
const int BMSK = 4e6;

void solve()
{
	ll x;cin >> x;
	// x * (x + 1) / 2 - (x + 1) * (x + 2) / 2 = 
	// x + 1 >= y * (y + 1) / 2
	
	ll r = 0 , l = 2000000000;
	while(l - r > 1)
	{
		ll mid = (l + r) / 2;
		if(mid * (mid + 1) / 2 <= x + 1) r = mid;
		else l = mid;
	}
	
	cout << x - r + 1 << '\n';
	
}

int main()
{
	ios::sync_with_stdio(0);
	cin.tie(0); cout.tie(0);

	/*int t;cin >> t;
	while(t--)*/
	solve();
}

#include <bits/stdc++.h>
using namespace std;

#define REP(i,n) for(ll i=0;i<(ll)n;i++)
#define dump(x)  cerr << "Line " << __LINE__ << ": " <<  #x << " = " << (x) << "\n";
#define spa << " " <<
#define fi first
#define se second
#define ALL(a)  (a).begin(),(a).end()
#define ALLR(a)  (a).rbegin(),(a).rend()

using ld = long double;
using ll = long long;
using ull = unsigned long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using pdd = pair<ld, ld>;

template<typename T> using V = vector<T>;
template<typename T> using P = pair<T, T>;
template<typename T> vector<T> make_vec(size_t n, T a) { return vector<T>(n, a); }
template<typename... Ts> auto make_vec(size_t n, Ts... ts) { return vector<decltype(make_vec(ts...))>(n, make_vec(ts...)); }
template<class S, class T> ostream& operator << (ostream& os, const pair<S, T> v){os << "(" << v.first << ", " << v.second << ")"; return os;}
template<typename T> ostream& operator<<(ostream &os, const vector<T> &v) { for (auto &e : v) os << e << ' '; return os; }
template<class T> ostream& operator<<(ostream& os, const vector<vector<T>> &v){ for(auto &e : v){os << e << "\n";} return os;}
struct fast_ios { fast_ios(){ cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;

template <class T> void UNIQUE(vector<T> &x) {sort(ALL(x));x.erase(unique(ALL(x)), x.end());}
template<class T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }
void fail() { cout << -1 << '\n'; exit(0); }
inline int popcount(const int x) { return __builtin_popcount(x); }
inline int popcount(const ll x) { return __builtin_popcountll(x); }
template<typename T> void debug(vector<vector<T>>&v,ll h,ll w){for(ll i=0;i<h;i++)
{cerr<<v[i][0];for(ll j=1;j<w;j++)cerr spa v[i][j];cerr<<"\n";}};
template<typename T> void debug(vector<T>&v,ll n){if(n!=0)cerr<<v[0];
for(ll i=1;i<n;i++)cerr spa v[i];
cerr<<"\n";};

const ll INF = (1ll<<62);
// const ld EPS   = 1e-10;
// const ld PI    = acos(-1.0);
const ll mod = (int)1e9 + 7;
//const ll mod = 998244353;

int main(){

    ll n;
    cin >> n;

    ll sqn = sqrt(2*(n+1));

    ll k = 0;
    for(ll i=-10;i<=10;i++){
        ll v = sqn + i;
        if(v<0) continue;
        if(v*(v+1) <= 2*(n+1)) chmax(k, v);
    }

    // dump(k)

    cout << n+1 - k << endl;

    return 0;
}