#include <fstream>
using namespace std;
int main()
{
    long long n=0,p,i;
    ifstream in ("fact.in");
    ofstream out("fact.out");
    in>>p;
    i=5;
    while (n<p)
    {
        n+=i/5;
        i+=5;
    }
    if (p)
    out<<i-5;
    else out<<1;
    return 0;
}