#include <fstream>

using namespace std;

ifstream in ("fact.in");
ofstream out ("fact.out");

int main()
{
    long long p,q,cnt=0,i;
    in>>p;
    for(i=0;i<=10000000;i++)
    {
        cnt+=i/5;
        if(cnt>=p)
        {
            out<<i*5;
            return 0;
        }
    }
    return 0;
}