#include <stdio.h>
#include <stdlib.h>
int i,j,n,m,k;
int v[5005];
int x[5005];
int aux[5005];
int rest[5005];
int rez[5005];
int decod (char c)
{
if (c=='0') return 0;
if (c=='1') return 1;
if (c=='2') return 2;
if (c=='3') return 3;
if (c=='4') return 4;
if (c=='5') return 5;
if (c=='6') return 6;
if (c=='7') return 7;
if (c=='8') return 8;
if (c=='9') return 9;
return 11;
}
void readdata()
{
FILE *f=stdin;
char c,ce;
fscanf(f,"%c",&c);
while (!feof(f)&&decod(c)<10)
 {
 ce=c;
 v[0]++;
 v[v[0]]=decod(ce);
 fscanf (f,"%c",&c);
 }
if (v[0]==1&&v[1]==0)
 {
 printf ("0");
 exit(0);
 }
for (i=1;i<=v[0]/2;i++)
{
 k=v[i];
 v[i]=v[v[0]-i+1];
 v[v[0]-i+1]=k;
 }
for (i=1;i<=v[0];i++)
 v[i]*=8;
for (i=1;i<v[0];i++)
 {
 v[i+1]+=v[i]/10;
 v[i]%=10;
 }
if (v[i]>=10)
 {
 v[0]++;
 v[i+1]+=v[i]/10;
 v[i]%=10;
 }
i=1;
while (v[i]==9)
 {
 v[i]=0;
 i++;
 }
v[i]++;
if (v[v[0]]==10)
 {
 v[0]++;
 v[v[0]-1]=0;
 v[v[0]]=1;
 }
fclose (f);
}
void inmult2()
{
aux[0]=0;
int re=0;
aux[0]=1;
aux[1]=0;
for (i=n;i>0;i--)
 {
 aux[0]++;
 aux[n-i+2]=x[i]*2+re;
 if (aux[n-i+2]>9) re=1,aux[n-i+2]%=10;
 else re=0;
 }
if (re>0) aux[0]++,aux[aux[0]]=1;
}
int bun(int cifr)
{
aux[1]=cifr;
int re=0;
rez[0]=0;
for (j=1;j<=aux[0];j++)
 {
 rez[0]++;
 rez[j]=aux[j]*cifr+re;
 re=rez[j]/10;rez[j]%=10;
 }
if (re>0)
    rez[0]++,rez[rez[0]]=re;
for (j=rez[0]+1;j<=rest[0];j++) rez[j]=0;
for (j=1;j<=rest[0];j++)
 {
 if (rest[j]>rez[rest[0]-j+1]) return 1;
 if (rest[j]<rez[rest[0]-j+1]) return 0;
 }
return 1;
}
void scade()
{
for (j=1;j<=rez[0];j++)
 {
 if (rest[rest[0]-j+1]<rez[j])
  {
  rest[rest[0]-j+1]+=10;
  i=j+1;
  while (rest[rest[0]-i+1]==0)rest[rest[0]-i+1]=9,i++;
  rest[rest[0]-i+1]--;
  }
 rest[rest[0]-j+1]-=rez[j];
 }
}
void writedata()
{
FILE *f=stdout;
for (i=v[0];i>0;i--)
 fprintf (f,"%d",v[i]);
fclose(f);
}
int main()
{
readdata();
n=1;
k=0;
m=0;

if (v[0]%2==1) m=v[v[0]],k=v[0]-1;
else m=v[v[0]]*10+v[v[0]-1],k=v[0]-2;
for (i=1;i*i<=m;i++);
i--;
x[1]=i;
m=m-i*i;
rest[0]=2;
rest[1]=m/10%10;
rest[2]=m%10;
for (k=k;k>0;k-=2)
 {
 rest[0]++;
 rest[rest[0]]=v[k];
 rest[0]++;
 rest[rest[0]]=v[k-1];
 inmult2();
 for (i=9;i>=0;i--)
  if (bun(i)==1)  break;
 n++;
 x[n]=i;
 scade();
 }
for (i=1;i<=n/2;i++)
 {
 k=x[i];
 x[i]=x[n-i+1];
 x[n-i+1]=k;
 }
i=1;
while (x[i]==0)
 {
 x[i]=9;
 i++;
 }
x[i]--;
if (x[n]==0) n--;
for (i=0;i<=1000;i++) v[i]=0;
if (x[n]>1) v[0]=n;
else v[0]=n-1;
k=0;
for (i=n;i>0;i--)
 {
 k+=x[i];
 v[i]=k/2;
 k=k%2;
 k*=10;
 }
writedata();
return 0;
}