#include <bits/stdc++.h>
using namespace std;
const int MC = 271;
struct Big {
int len, V[MC];
void read() {
string s;
cin >> s;
len = s.size();
for(int i = len; i >= 1; --i)
V[i] = s[len - i] - '0';
}
Big() {
len = 0;
memset(V, 0, sizeof(V));
}
void pune(int v) {
len = 0;
memset(V, 0, sizeof(V));
while (v)
V[++len] = v % 10, v /= 10;
}
void ref() {
int tr = 0;
for (int i = 1; i <= len; ++i) {
V[i] += tr;
tr = 0;
if (V[i] >= 10)
tr = V[i] / 10;
else if (V[i] < 0){
while(V[i] < 0)
--tr, V[i] = V[i] + 10;
}
V[i] %= 10;
}
while (tr) V[++len] = tr % 10, tr /= 10;
while (len && !V[len]) --len;
}
Big operator*(const Big &b) const {
Big re;
for (int i = 1; i <= len; ++i)
for (int j = 1; j <= b.len; ++j)
re.V[i + j - 1] += V[i] * b.V[j];
re.len = len + b.len - 1;
re.ref();
return re;
}
Big operator*(const int &v) const {
Big re;
for (int i = 1; i <= len; ++i)
re.V[i] += V[i] * v;
re.len = len;
re.ref();
return re;
}
Big operator/(const int &v) const {
Big re;
int tr = 0;
re.len = len;
for (int i = len; i >= 1; --i)
tr += V[i], re.V[i] = tr / v, tr %= v, tr *= 10;
re.ref();
return re;
}
Big operator+(const int &v) const {
Big re;
re = (*this);
re.V[1] += v;
re.ref();
return re;
}
Big operator-(const int &v) const {
Big re;
re = (*this);
re.V[1] -= v;
re.ref();
return re;
}
Big operator+(const Big &b) const {
Big re;
re.len = max(len, b.len);
for(int i = 1; i <= len; ++i) re.V[i] += V[i];
for(int i = 1; i <= b.len; ++i) re.V[i] += b.V[i];
re.ref();
return re;
}
Big operator-(const Big &b) const {
Big re;
re.len = max(len, b.len);
for(int i = 1; i <= len; ++i) re.V[i] += V[i];
for(int i = 1; i <= b.len; ++i) re.V[i] -= b.V[i];
re.ref();
return re;
}
bool operator <(const Big &b) const {
if(len != b.len) return len < b.len;
for(int i = len; i >= 1; --i)
if(V[i] != b.V[i]) return V[i] < b.V[i];
return 0;
}
Big(int v) {
pune(v);
}
void afis() {
for(int i = len; i >= 1; --i)
cout << V[i];
cout << "\n";
}
};
int main() {
Big n, st(1), dr, mij, t1, t2;
n.read();
dr = n;
while (st < dr) {
mij = (st + dr + 1) / 2;
t1 = mij * (mij + 1);
t2 = n * 2;
if (t1 < t2) st = mij;
else dr = mij - 1;
}
Big re = n * 2;
re = re - st;
re = re - 1;
if(!re.len) re.len = re.V[1] = 1;
re.afis();
return 0;
}
