#include <iostream>
#include <fstream>
using namespace std;
int t[100000];
int main()
{
    ifstream fin("fact.in");
    ofstream fout("fact.out");
    long long int i,N,P,st,dr,mid,contor=0;
    st=1;
    dr=2e9;
    fin>>P;
    while(st<=dr)
    {
        contor=0;
        mid=(st+dr)/2;
        for(i=5;i<=mid;i*=5)
        {
            contor+=mid/i;
        }
        if(contor>=P)
        {
            dr=mid-1;
        }
        else
        {
            st=mid+1;
        }
    }
    mid=st;
    contor=0;
    for(i=5;i<=mid;i*=5)
    {
        contor+=mid/i;
    }
    if(P==contor)
        fout<<mid;
    else
        fout<<-1;

    return 0;
}