//#include <iostream>
#include <fstream>
using namespace std;

int main()
{
    ifstream cin("fact.in");
    ofstream cout("fact.out");
    long long p;
    cin>>p;
    long long st=1,dr=1000000000000000000,sol;
    while(st<=dr){
        long long mid=(st+dr)/2,sum=0;
        long long x=mid;
        while(x){
            sum+=x/5;
            x/=5;
        }
        if(sum>=p){
            sol=mid;
            dr=mid-1;
        }
        else{
            st=mid+1;
        }
    }
    long long sum=0,cp=sol;
    while(cp){
        sum+=cp/5;
        cp/=5;
    }
    if(sum==p){
        cout<<sol;
    }
    else
        cout<<-1;
    return 0;
}