#include <bits/stdc++.h>

#define INfile "fact.in"
#define OUTfile "fact.out"

using namespace std;

ifstream fin(INfile);
ofstream fout(OUTfile);

long long p;

int nr5(int nr)
{
    int s=0,p=5;
    while(nr>=p)
    {
        s+=nr/p;
        p*=5;
    }
    return s;
}

int cb(int st, long long dr, int p)
{
int poz=-1,mij;
    while(st<=dr)
    {
        mij=(st+dr)/2;
        if(nr5(mij)==p)
        {
            poz=mij;
            dr=mij-1;
        }
        if(nr5(mij)<p)
            st=mij+1;
        else
            dr=mij-1;
    }
    return poz;
}

int main()
{
    fin>>p;
    fout<<cb(1,500000000,p);
    return 0;
}