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



long long  zero(long long x)
{
    long long S=0;
    for(long long i=5;x/i>0;i*=5)
        S+=x/i;
    return S;
}
long long binarysearch(long long x)
{
    long long a=1, b=100000000, c;
    while(a<=b)
    {
        c=(a+b)/2;
        if(zero(c)<x)
            a=c+1;
        else
            b=c-1;

    }
    if(zero(a)==x)
        return a;
    else
        return -1;
}
int main()
{long long p;
ifstream r("fact.in");
ofstream g("fact.out");
    r>>p;
    g<<binarysearch(p);


    return 0;
}