#include <iostream>
#include <fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int k, out=-1;
long long sum, mid, st=1, dr=1<<29;
void check(int a)
{
    sum=0;
    while(a)
    {
        sum+=a/5;
        a/=5;
    }
}

void bin_src()
{
    while(st<=dr)
    {
        mid=(st+dr)/2;
        check(mid);
        if(sum==k)
            out=mid;
        if(sum>=k) dr=mid-1;
        else st=mid+1;
    }
}

int main()
{
    f>>k;
    bin_src();
    g<<out;
    return 0;
}