#include<bits/stdc++.h>
using namespace std;
#define re register
#define in inline
#define get getchar()
#define ll long long
int main()
{
	ll n;
	cin>>n;
	if(n<=2) cout<<1<<endl;
	else
	{
		ll l=2,r=sqrt(2*n),mid,ans;
		while(l<=r)
		{
			mid=l+r>>1;
			if((2+mid)*(mid-1)/2<=n) ans=mid, l=mid+1;
			else r=mid-1;
		}
		cout<<2+((n-1)-ans)<<endl;
	}
}

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

#define int long long
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define rep(i, n) for (int i = 0; i < n; ++i)
#define rep1(i, n) for (int i = 1; i < n; ++i)
#define exrep(i, a, b) for (ll i = a; i < b; i++)
#define out(x) cout << x << endl
#define EPS (1e-7)
#define gearup                    \
    ios_base::sync_with_stdio(0); \
    cin.tie(0);                   \
    cout.tie(0);

typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef vector<char> vc;
typedef vector<bool> vb;
typedef vector<double> vd;
typedef vector<string> vs;
typedef vector<pair<int, int>> vpii;
typedef vector<vector<int>> vvi;
typedef vector<vector<char>> vvc;
typedef vector<vector<bool>> vvb;
typedef vector<vector<double>> vvd;
typedef vector<vector<string>> vvs;
typedef vector<ll> vl;
typedef vector<vector<ll>> vvl;
typedef vector<vector<vector<ll>>> vvvl;
ll MOD = 1000000007;
const long long L_INF = 1LL << 60;
const int INF = 2147483647; // 2^31-1
const double PI = acos(-1);
//cout<<fixed<<setprecision(10);

template <class T>
inline bool chmin(T &a, T b)
{
    if (a > b)
    {
        a = b;
        return true;
    }
    return false;
}
template <class T>
inline bool chmax(T &a, T b)
{
    if (a < b)
    {
        a = b;
        return true;
    }
    return false;
}
template <class T>
void debug(T v)
{
    rep(i, v.size()) cout << v[i] << " ";
    cout << endl;
}
const ll dx[8] = {1, 1, 0, -1, -1, -1, 0, 1};
const ll dy[8] = {0, 1, 1, 1, 0, -1, -1, -1};
//以降 cin の入力元が 'input.txt' になる
//std::ifstream in("input.txt");
//std::cin.rdbuf(in.rdbuf());

signed main()
{
    gearup;
    ll n;
    cin >> n;
    ll ma = 1e9 * 2 + 10, mi = 0;
    while (ma - mi > 1)
    {
        ll mid = (ma + mi) / 2;
        // 1 ~ midまでの数が作れるか
        ll ttl = mid * (1 + mid) / 2;
        if (ttl <= n + 1)
            mi = mid;
        else
            ma = mid;
    }
    out(n - ma + 2);
}
