#include <iostream>
#include <math.h>
#include <fstream>
using namespace std;

int main()
{
    unsigned long long p,n,i,k,x=0,l;
    ifstream f("fact.in");
    ofstream g("fact.out");
        f>>p;
    if (p==1)
        g<<0;
    else
    {n=10;k=1;
    while (!x)
    {k=0;
            i=1;l=5;
            while (l<=n)
                {
                    k=int(n/l+k);
                    i++;
                    l=pow(5.,i);
                }
            if (k==p)
            {g<<n;
            x=1;
            }

    n=n+5;
    }
    }

}