#include<cstdio>
using namespace std;
int z0(int x)
{
    int nr=0, imp=5;
    while(x>=imp)
    {
        nr=nr+x/imp;
        imp=imp*5;
    }
    return nr;
}
int caut(int st,int dr,int p)
{
    st=1;
    int nr=-1;
    while(st<=dr)
    {
        int m=st+(dr-st)/2;
        if (z0(m)==p) nr=m;
        if (z0(m)>=p) dr=m-1;
        else st=m+1;
    }
    return nr;
}
int main()
{
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
    int p,nr;
    scanf("%d",&p);
    if (p==0)
    {
        printf("1");
    }
    else
    {
        nr=caut(1,p*5,p);
        printf("%d",nr);
    }
    return 0;
}