#include <bits/stdc++.h>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int p;
int Check(int x)
{
    int q=5,p,cnt=0;
    while(q<=x)
    {
        cnt+=(x/q);
        q*=5;
    }
    return cnt;
}
int Cb(int p)
{
    int st,dr,mij,x,sol=-1;
    st = 1;
    dr = 1e9;
    while (st <= dr)
    {
        mij = (st + dr) / 2;
        x = Check(mij);
        if (x == p)
        {
            sol = mij;
            dr = mij - 1;
        }
        else if (x > p) dr = mij - 1;
        else st = mij + 1;
    }
    return sol;

}
int main()
{
    fin >> p;
    fout<<Cb(p)<<" ";
    return 0;
}