#include<iostream>
#include<algorithm>
#include<cctype>
#include<cstring>
#include<cstdlib>
#include<vector>
#include<string>
#include<cmath>
using namespace std;
#define REP(i, j) for(int i = 0; i < j; i++)
#define FOR(i, j, k) for(int i = j; i < k; i++)
const double EPS = 1e-8;
const int INF = 1e9;

int main(){
    double vv;
    while(cin >>vv){
        double v = 9.8, t = 1, y;
        for(y = 5; v < vv; y += 5){
            t = sqrt(y / 4.9);
            v = 9.8 * t;
        }
        cout <<y / 5 <<endl;
    }
    return 0;
}