#include <iostream>
#include <cstdio>
#include <math.h>

using namespace std;

int main(void){
    double v;
    
    while (cin>>v)
    {
        double n,k;
        n = (4.9*(v/9.8)*(v/9.8)+5)/5;
        //cout<<"n="<<n<<endl;
        k=n-(int)n;
        if(0.5<=k){n+=1-k;}
        else {n-=k;}
        cout<<n<<endl;
    }
    return 0;
}