#include <bits/stdc++.h>

using namespace std;

ifstream f("fact.in");
ofstream g("fact.out");

long long p;

int fact(int n)
{
    long long s=0;
    while(n>=5)
        s+=n/5, n/=5;
    return s;
}

int cautbin(int n)
{
    int st=0,m,dr=1000000000;
    while(st<dr)
    {
        m=(st+dr)/2;
        if(fact(m)>p) dr=m;
        else st=m+1;
    }
    st-=5;
    return st;
}


int main()
{
    f>>p;
    if(p==0)
        g<<1;
    else if(fact(cautbin(p))!=p)
        g<<-1;
    else g<<cautbin(p);
}