#include<iostream.h>
#include<string.h>
#define MAX 2000
    int srav(int a[MAX+100],int b[MAX+100]);
    int sqr();
    int pr[MAX+100],result[MAX+100];
void main(){
    char str[MAX+100];
    int t,j,p[MAX+100],q[MAX+100],mass[MAX+100];
    for(int i=0;i<MAX;i++)
    {
        mass[i]=0;
        str[i]=0;
        p[i]=0;
        q[i]=0;
    }
    cin >> str;
    //for(i=MAX-1;i>=0;i--)
    //    if(str[i])
    int pm=strlen(str);
    if((pm==1)&&(str[0]=='0'))
    {
        cout << 0;
        return ;
    }
    for(i=0;i<pm;i++)
         mass[i]=int(str[pm-i-1])-48;
    int l=0;
    for(i=0;i<MAX;i++)
    {
        t=mass[i];
        mass[i]=(t*2+l)%10;
        l=(t*2+l)/10;
    }
    for(i=MAX-1;i>=0;i--)
        if(mass[i]!=0)
        {
            pm=i+1;
            break;
        }
    q[pm/2+1]=1;
    while(srav(p,q)==1)
    {
        for(i=MAX-1;i>=0;i--)
            pr[i]=0;
        l=0;
        for(i=0;i<MAX;i++)
        {
            pr[i]=(p[i]+q[i]+l)%10;
            l=(p[i]+q[i]+l)/10;
        }
        for(i=MAX-1;i>=0;i--)
            if(pr[i]!=0)
            {
                for(j=i;j>0;j--)
                {
                    if(pr[j]%2!=0)
                        pr[j-1]+=10;
                    pr[j]/=2;
                }
                pr[0]/=2;
                break;
            }
        l=sqr();
        if(l>pm)
            for(i=0;i<MAX;i++)
                q[i]=pr[i];
        if(l<pm)
            for(i=0;i<MAX;i++)
                p[i]=pr[i];
        if(l==pm)
        {
            if(srav(result,mass)==1)
                for(i=0;i<MAX;i++)
                    p[i]=pr[i];
            if(srav(result,mass)==0)
                break;
            if(srav(result,mass)==-1)
                for(i=0;i<MAX;i++)
                    q[i]=pr[i];
        }
    }
    for(i=MAX-1;i>=0;i--)
        if(pr[i]!=0)
        {
            for(j=i;j>=0;j--)
                cout << pr[j];
            break;
        }
}
int srav(int a[MAX],int b[MAX]){
    for(int i=MAX-1;i>=0;i--)
    {
        if(a[i]<b[i])
            return 1;
        if(a[i]>b[i])
            return -1;
    }
    return 0;
}
int sqr(){
    int l,i,j,t;
    for(i=MAX-1;i>=0;i--)
        if(pr[i]!=0)
        {
            l=i+1;
            break;
        }
    for(i=MAX-1;i>=0;i--)
        result[i]=0;
    for(i=0;i<l;i++)
        for(j=0;j<l;j++)
            if(i+j<MAX-5)
            {
                t=pr[i]*pr[j];
                result[i+j]+=t;
            }
            else
                return MAX+200;
    l=0;
    for(i=0;i<MAX-1;i++)
    {
        t=result[i];
        result[i]=(result[i]+l)%10;
        l=(t+l)/10;
    }
    if(l!=0)
        return MAX+200;
    l=0;
    for(i=0;i<MAX;i++)
    {
        t=result[i];
        result[i]=(l+result[i]+pr[i])%10;
        l=(l+t+pr[i])/10;
    }
    if(l!=0)
        return MAX+200;
    for(i=MAX-1;i>=0;i--)
        if(result[i]!=0)
            return i+1;
    return 0;
}