#include<fstream>
#include<iostream>
#include<climits>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int main()
{
    int m,p,i=1,k,OK=0,x,j=LONG_MAX;
    fin>>p;
    if(p==0)fout<<"1";
    while(i<=j&&OK==0){m=(i+j)/2;
                        x=5;
                        k=0;
                        while(x<=m){k=k+m/x;
                        x=x*5;}
                        if(k==p)OK=1;
                        else if(k>p)j=m-1;
                        else i=m+1;
    }
    if(OK==0)fout<<"-1";
    else {
        while(m%5!=0)m--;
        fout<<m;
        }
    fin.close();
    fout.close();
    return 0;
}