#include <bits/stdc++.h>

using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
typedef long long ll;
ll zero(ll x)
{
    ll P=5;
    ll S=0;
    while(P<=x) S+=x/P,P*=5;
    return S;
}
int main()
{
    ll p,st,dr,mij;
    fin>>p;
    st=-1;
    dr=1<<62;
    while(dr>st+1)
    {
        mij=(st+dr)/2;
        if(zero(mij)<p) st=mij;
        else dr=mij;
    }
    if(zero(dr)==p) fout<<dr<<"\n";
    else fout<<"-1\n";
    return 0;
}