#include <math.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define USE 4
#define INF 10000
#define MAX 500
typedef struct {int num[MAX], len;
}bignum;
char str[1000];
bignum a, b, c;void add(bignum *a, int k)
{int i;for(i = 1; i <= a->len; i++){if(!k){break;}a->num[MAX - i] += k;k = a->num[MAX - i] / INF;a->num[MAX - i] %= INF;}if(k){a->num[MAX - i] = k;a->len++;}
}void dec(bignum *a, bignum *b)
{int i, j = 0;int len = b->len;for(i = 1; i <= len; i++){a->num[MAX - i] = a->num[MAX - i] - b->num[MAX - i] - j;j = 0;while(a->num[MAX - i] < 0){a->num[MAX - i] += INF;j++;}}if(j){a->num[MAX - i] -= j;}for(i = a->len; i >= 1; i--){if(a->num[MAX - i]){break;}}a->len = i;
}void mul(bignum *a, int k)
{int i, j = 0;//考虑一个特殊情况, k=0时if(k == 0){memset(a, 0, sizeof(bignum));return;}for(i = 1; i <= a->len; i++){a->num[MAX - i] = a->num[MAX - i] * k + j;j = a->num[MAX - i] / INF;a->num[MAX - i] %= INF;}if(j){a->num[MAX - i] = j;a->len++;}
}void output(bignum *a)
{int i;printf("%d", a->num[MAX - a->len]);for(i = a->len - 1; i >= 1; i--){printf("%.*d", USE, a->num[MAX - i]);}printf("\n");
}int com(bignum *a, bignum *b)
{int i;if(a->len != b->len){return a->len - b->len;}for(i = a->len; i >= 1; i--){if(a->num[MAX - i] != b->num[MAX - i]){return a->num[MAX - i] - b->num[MAX - i];}}return 0;
}int getnum(int len)
{static int start = 0;int i, n = 0;for(i = 0; i < len; i++){n *= 10;n += str[start + i] - '0';}start += len;return n;
}int check(int k)
{memcpy(&c, &b, sizeof(b));//c = (20 * b + k) * k;mul(&c, k * 20);add(&c, k * k);if(com(&a, &c) >= 0){return 1;}return 0;
}int main(int argc, char **argv)
{int i, j, t, n;scanf("%s", str);n = strlen(str);if(n & 1){j = getnum(1);}else{j = getnum(2);}n = (n + 1) / 2;t = sqrt(j);add(&a, j - t * t);add(&b, t);for(i = 2; i <= n; i++){mul(&a, 100);add(&a, getnum(2));for(j = 9; j >= 0; j--){if(check(j)){break;}}dec(&a, &c);mul(&b, 10);add(&b, j);}output(&b);return 0;
}