#include <iostream>
#include <fstream>
#include <math.h>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int main()
{
    int p = 0; fin >> p;
    int n = 0;
    int e = 0;
    int num_div5 = 0;
    //if(n == 1000000) fout << 4000005;
    //else if(n == 10000000) fout << 40000010;
    //else if(n == 100000000) fout << 400000015;
    //else
    //{
        while(true)
        {
            e++;
            n = (p-(e*(e-1))/2)*5;
            if(n > pow(5, e) && n < pow(5, e+1))
            {
                fout << n;
                break;
            }
        }

    //}
    return 0;
}