#include <bits/stdc++.h>
#define clr(x) memset(x,0,sizeof(x))
#define For(i,a,b) for (int i=(a);i<=(b);i++)
#define Fod(i,b,a) for (int i=(b);i>=(a);i--)
#define fi first
#define se second
#define kill _z_kill
#define y0 _z_y0
#define y1 _z_y1
#define x0 _z_x0
#define x1 _z_x1
#define pb push_back
#define mp(x,y) make_pair(x,y)
using namespace std;
typedef long long LL;
typedef unsigned long long ull;
typedef unsigned uint;
typedef long double LD;
typedef vector <int> vi;
typedef pair <int,int> pii;
void enable_comma(){}
string tostring(char c){
	string s="";
	s+=c;
	return s;
}
string tostring(string s){
	return "\""+s+"\"";
}
string tostring(const char *c){
	return tostring((string)c);
}
string tostring(long long x){
	if (x<0)
		return "-"+tostring(-x);
	if (x>9)
		return tostring(x/10)+tostring(char('0'+x%10));
	else
		return tostring(char('0'+x));
}
string tostring(int x){
	return tostring((long long)x);
}
string tostring(unsigned long long x){
	if (x>9)
		return tostring((long long)(x/10))+tostring(char('0'+x%10));
	else
		return tostring(char('0'+x));
}
string tostring(unsigned x){
	return tostring((long long)x);
}
string tostring(double x){
	static char res[114];
	sprintf(res,"%lf",x);
	string s=tostring(res);
	return s.substr(1,(int)s.size()-2);
}
string tostring(long double x){
	return tostring((double)x);
}
template <class A,class B> string tostring(pair <A,B> p){
	return "("+tostring(p.fi)+","+tostring(p.se)+")";
}
template <class T> string tostring(T v){
	string res="";
	for (auto p : v)
		res+=(res.size()?",":"{")+tostring(p);
	return res.size()?res+"}":"{}";
}
template <class A> string tostring(A* a,int L,int R){
	return tostring(vector <A>(a+L,a+R+1));
};
template <class A> string tostring(A a,int L,int R){
	return tostring(a.data(),L,R);
}
string tostrings(){
	return "";
}
template <typename Head,typename... Tail>
string tostrings(Head H,Tail... T){
	return tostring(H)+" "+tostrings(T...);
}
#define User_Time ((double)clock()/CLOCKS_PER_SEC)
#ifdef zzd
	#define outval(x) cerr<<#x" = "<<tostring(x)<<endl
	#define outvals(...) cerr<<"["<<#__VA_ARGS__<<"]: "<<\
								tostrings(__VA_ARGS__)<<endl
	#define outtag(x) cerr<<"--------------"#x"---------------"<<endl
	#define outsign(x) cerr<<"<"#x">"<<endl
	#define outarr(a,L,R) cerr<<#a"["<<(L)<<".."<<(R)<<"] = "<<\
								tostring(a,L,R)<<endl
#else
	#define outval(x) enable_comma()
	#define outvals(...) enable_comma()
	#define outtag(x) enable_comma()
	#define outsign(x) enable_comma()
	#define outarr(a,L,R) enable_comma()
#endif
#ifdef ONLINE_JUDGE
	#ifdef assert
		#undef assert
	#endif
	#define assert(x) (!(x)?\
			cout<<"Assertion failed!"<<endl<<\
			"function: "<<__FUNCTION__<<endl<<\
			"line: "<<__LINE__<<endl<<\
			"expression: "<<#x<<endl,exit(3),0:1)
#endif
LL read(){
	LL x=0,f=0;
	char ch=getchar();
	while (!isdigit(ch))
		f=ch=='-',ch=getchar();
	while (isdigit(ch))
		x=(x<<1)+(x<<3)+(ch^48),ch=getchar();
	return f?-x:x;
}
template <class T> void ckmax(T &x,const T y){
	if (x<y)
		x=y;
}
template <class T> void ckmin(T &x,const T y){
	if (x>y)
		x=y;
}
//int Pow(int x,LL y){
////	y=(y%(mod-1)+(mod-1))%(mod-1);
//	int ans=1;
//	for (;y;y>>=1,x=(LL)x*x%mod)
//		if (y&1)
//			ans=(LL)ans*x%mod;
//	return ans;
//}
//void Add(int &x,int y){
//	if ((x+=y)>=mod)
//		x-=mod;
//}
//void Del(int &x,int y){
//	if ((x-=y)<0)
//		x+=mod;
//}
//int Add(int x){
//	return x>=mod?x-mod:x;
//}
//int Del(int x){
//	return x<0?x+mod:x;
//}
//int md(LL x){
//	return (x%mod+mod)%mod;
//}
int main(){
	LL n=read();
	LL ans=n;
	LL v=n+1;
	LL L=2,R=2e9;
	while (L<=R){
		LL mid=(L+R)>>1;
		if (mid*(mid+1)/2<=v)
			L=mid+1,ans=n-mid+1;
		else
			R=mid-1;
	}
	cout<<ans<<endl;
	return 0;
}

#include <bits/stdc++.h>
#include <string>
#define MAX 100007
#define scn1(a) scanf("%d", &a);
#define scn2(a, b) scanf("%d %d", &a, &b);
#define scn3(a, b, c) scanf("%d %d %d", &a, &b, &c);
#define lscn1(a) scanf("%lli", &a);
#define lscn2(a, b) scanf("%lli %lli", &a, &b);
#define lscn3(a, b, c) scanf("%lli %lli %lli", &a, &b, &c);
#define prnt(a) printf("%d\n", a);
#define forr(i, a, n) for(int i=a;i<n;i++)
#define nl puts("");
#define PB push_back
#define enl cout << "\n";
#define CHK(a) cout << (#a) << " = " << (a) << endl;
typedef long long int ll;
using namespace std;
void arraychk(int a[],int n) {for(int i=0;i<n;i++)cout<<a[i]<<" ";enl;}
#define LOOPCHK(a, n) arraychk(a, n);

int main()
{
    #ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
    #endif
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    ll tt=1;
    // cin >> tt;
    for(int cse=1; cse<=tt; cse++)

    {
        ll i=0, j=0, k=0, l=0, m=0,
        n=0, x=0, y=0, ans=0, sum=0;
        
        cin >> n;
        m = sqrt( n+1 );
        while( m*m + m <= 2*(n+1) ) m++;
        m--;
        // cout << "Case " << cse <<  ":";
        cout << n-m+1 << endl;
    }
    return 0;
}
