#include <bits/stdc++.h>

using namespace std;

#define ll long long
#define ull unsigned long long
#define intmax 0x7fffffff
#define halfintmax 0x3fffffff

typedef pair<int, int> pii;
typedef pair<int, char> pic;

const int N = 200009;
const int mod = 998244353;

ll n;

int main() {
    cin >> n;
    ll l = 0, r = 1.5e9;
    while(l < r) {
        ll mid = l + r + 1 >> 1;
        if(mid * (mid + 1) / 2 <= n + 1) l = mid;
        else r = mid - 1;
    }
    cout << n - l + 1;
    return 0;
}


#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp> 
#include <ext/pb_ds/tree_policy.hpp> 
using namespace std;
using namespace __gnu_pbds; 
#define gc getchar_unlocked
#define fo(i,n) for(int i=0;i<n;i++)
#define Fo(i,k,n) for(int i=k;k<n?i<n:i>n;k<n?i+=1:i-=1)
#define ll long long int
#define s(x)	cin>>x
#define p(x)	cout<<x<<"\n"
#define goog(x, y)  cout<<"Case #"<<x<<": "<<y<<"\n"
#define pb push_back
#define mp make_pair
#define F first
#define S second
#define all(x) x.begin(), x.end()
#define clr(x) memset(x, 0, sizeof(x))
#define sortall(x) sort(all(x))
#define tr(it, a) for(auto it = a.begin(); it != a.end(); it++)
#define PI 3.1415926535897932384626
#define INF 100000000000
#define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update> 
typedef pair<int, int>	pii;
typedef pair<ll, ll>	pl;
typedef vector<int>		vi;
typedef vector<ll>		vl;
typedef vector<pii>		vpi;
typedef vector<pl>		vpl;
typedef vector<vi>		vvi;
typedef vector<vl>		vvl;
typedef long double ld;

mt19937_64 rang(chrono::high_resolution_clock::now().time_since_epoch().count());
int rng(int lim) {
	uniform_int_distribution<int> uid(0,lim-1);
	return uid(rang);
}
int mpow(int base, int exp); 
void ipgraph(int n, int m);
int gcd(int a, int b) ;

const int mod = 1'000'000'007;
const int N = 3e5, M = N;
//=======================

vi g[N];
int a[N];

void solve() {
  ll n;cin>>n;
  //ll tp=1e9+1e8;
  ll tp=2*floor(sqrt(n));
  ll res;
  ll st=0;
  while(st<=tp)
  { ll m=(st+tp)/2;
    if(m*(m+1)<=2*(n+1))
    {res=m;st=m+1;}
    else
    tp=m-1;
  }
  p(n+1-res);
  
}

int main() {
    ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    srand(chrono::high_resolution_clock::now().time_since_epoch().count());

    int t = 1;
    //cin >> t;
    while(t--) {
      solve();
    }

    return 0;
}

int mpow(int base, int exp) {
  base %= mod;
  int result = 1;
  while (exp > 0) {
    if (exp & 1) result = ((ll)result * base) % mod;
    base = ((ll)base * base) % mod;
    exp >>= 1;
  }
  return result;
}

void ipgraph(int n, int m){
	int i, u, v;
	while(m--){
		cin>>u>>v;
    //u--, v--;
		g[u].pb(v);
		g[v].pb(u);
	}
}


int gcd(int a, int b) 
{ 
    if (a == 0) 
        return b; 
    return gcd(b % a, a); 
} 