#include <bits/stdc++.h>
using namespace std;
long long p;

long long zero(long long x)
{
    long long c=0;
    for(long long i=5;x/i>0;i*=5)
        c+=x/i;
    return c;
}

long long cb(long long x)
{
    long long st=1,dr=10000000010,mid;
    while(st<=dr)
    {
        mid=(st+dr)/2;
        if(zero(mid)<x) st=mid+1;
        else dr=mid-1;
    }
    if(zero(st)==x) return st;
    else return -1;

}

int main()
{
    ifstream cin("fact.in");
    ofstream cout("fact.out");
    cin>>p;
    cout<<cb(p);
    return 0;
}