#include <iostream>
#include <stdio.h>
using namespace std;
FILE*f=fopen("fact.in","r");
FILE*g=fopen("fact.out","w");
int main()
{
    int p,n,ok=0,x,st=5,dr,s,m,z=1;
    fscanf(f,"%d",&p);
    dr=5*p;
    while (ok==0&&st<=dr){
        m=(st+dr)/2;
        if (m%5!=0) m-=2;
        x=m/5; s=0;
        while (x){
            s+=x;
            x/=5;
        }
        if (s==p) {n=m; ok=1;}
        else if (s<p) st=m+5;
            else dr=m-5;
    }
    if (st>dr) n=-1;
    if (p!=0) fprintf(g,"%d",n);
    else fprintf(g,"1");
    fclose(f);
    fclose(g);
    return 0;
}