sqrt

#include <vector>

#include <list>

#include <map>

#include <set>

#include <deque>

#include <queue>

#include <stack>

#include <bitset>

#include <algorithm>

#include <functional>

#include <numeric>

#include <utility>

#include <sstream>

#include <iostream>

#include <iomanip>

#include <cstdio>

#include <cmath>

#include <cstdlib>

#include <cctype>

#include <string>

#include <cstring>

#include <ctime>

#include <fstream>

using namespace std;

#define maxlen 4000

void mul(int k, int a[], int *lena)

{

    for(int i = 0; i < *lena; i++)

        a[i] *= k;

    for(int i = 0; i < *lena; i++)

    {

        a[i + 1] += a[i] / 10;

        a[i] %= 10;

    }

    while(a[*lena])

    {

        a[*lena + 1] += a[*lena] / 10;

        a[*lena] %= 10;

        (*lena)++;

    }

    return;

}

bool judge(int a[], int lena, int b[], int lenb)

{

    if(lena < lenb)

        return 0;

    for(int i = lena - 1; i >= 0; i--)

        if(a[i] > b[i])

            return 1;

        else if(a[i] < b[i])

            return 0;

    return 0;

}

bool func(int m, int nr[], int lennr, int R[], int lenR)

{

    mul(20 * m, nr, &lennr);

    nr[0] += m * m;

    lennr = max(lennr, 1);

    for(int i = 0; i < lennr; i++)

    {

        nr[i + 1] += nr[i] / 10;

        nr[i] %= 10;

    }

    while(nr[lennr])

    {

        nr[lennr + 1] += nr[lennr] / 10;

        nr[lennr] %= 10;

        lennr++;

    }

    return judge(nr, lennr, R, lenR);

}

void newR(int k, int r[], int lenr, int R[], int *lenR)

{

    mul(20 * k, r, &lenr);

    for(int i = 0; i < *lenR; i++)

    {

        R[i] -= r[i];

        if(!i)

            R[i] -= k * k;

        while(R[i] < 0)

        {

            R[i] += 10;

            R[i + 1]--;

        }

    }

    while(*lenR && !R[*lenR - 1])

        (*lenR)--;

    return;

}

int main()

{

    int N[maxlen], lenN, R[maxlen], lenR = 0, r[maxlen], lenr = 0;

    memset(N, 0, sizeof(N));

    memset(R, 0, sizeof(R));

    memset(r, 0, sizeof(r));

    string str;

    cin >> str;

    lenN = str.size();

    for(int i = lenN - 1; i >= 0; i--)

        N[i] = (char)str[lenN - 1 - i] - '0';

/*check the number

    for(int i = lenN - 1; i >= 0; i--)

        cout << N[i];

    cout << endl;

*/

    for(int i = lenN - 1; i >= 0; i--)

    {

        if(i & 1)

            continue;

        for(int j = lenR - 1; j >= 0; j--)

            R[j + 2] = R[j];

        R[1] = N[i + 1];

        R[0] = N[i];

        lenR += 2;

        while(lenR && !R[lenR - 1])

            lenR--;

        int k, nr[maxlen], lennr = lenr;

        for(k = 0; k < 10; k++)

        {

            memcpy(nr, r, sizeof(nr));

            if(func(k + 1, nr, lennr, R, lenR))

                break;

        }

        memcpy(nr, r, sizeof(nr));

        newR(k, nr, lennr, R, &lenR);

        for(int j = lenr - 1; j >= 0; j--)

            r[j + 1] = r[j];

        r[0] = k;

        lenr++;

    }

    for(int i = lenr - 1; i >= 0; i--)

        cout << r[i];

    cout << endl;

    return 0;

}