#include <fstream>
#define xmax (1<<30)
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int p;
int put[15]={0,6,31,156,781,3906,19531,97656,488281,2441406,12207031,61035156,305175781};
int descomp(int x)
{
    int s=0;
    while(x>25)
    {
        int p1=5,nr=0;
        while(p1*5<=x)
            p1*=5,nr++;
        s+=put[nr];
        x-=p1;
    }
    if(x==25)
        s+=6;
    else s+=x/5;
    return s;
}
int caut_bin(int st,int dr)
{
    int mij=(st+dr)>>1;
    while(st<=dr)
    {
        if(descomp(mij)<p)
            st=mij+1;
        else if(descomp(mij)>p) dr=mij-1;
        else return mij;
        mij=(st+dr)>>1;
    }
    return -1;
}
void read()
{
    f>>p;
    int x=caut_bin(1,xmax);
    if(x==-1)
        g<<x<<'\n';
    else
    {
        while(x%5&&x>1)
            --x;
        g<<x<<'\n';
    }
}
int main(void)
{
    descomp(125);
    read();
}