#include<cstdio>
using namespace std;
FILE*in=fopen("fact.in","r");
FILE*out=fopen("fact.out","w");
int p,sol=-1,INF=1000000009,p5[]={1,5,25,125,625,3125,15625,78125,390625,1953125,9765625,48828125,244140625};
int ok(int d)
{
    int y=0,f;
    for(int i=1;i<13;i++)
    {
        f=d/p5[i];
        y+=f;
    }
    return y;
}
void bs()
{
    int st=1,dr=INF,mij,val;
    while(st<=dr)
    {
        mij=(st+dr)/2;
        val=ok(mij);
        if(val>=p)
        {
            if(val==p)
            {
                sol=mij;
            }
            dr=mij-1;
        }
        else
        {
            st=mij+1;
        }
    }
}
int main()
{
    fscanf(in,"%d",&p);
    bs();
    fprintf(out,"%d",sol);
}