#include <cstdio>
#define  NMax 500000001
using namespace std;
int mijloc,stg,dr,p,copie;
int zerouri(int x)
{
    int p=5,nr=0;
    while(x/p)
    {
        nr+=x/p;
        p=p*5;
    }
    return nr;
}

int main()
{
    freopen("factorial.in","r",stdin);
    freopen("factorial.out","w",stdout);
    scanf("%d",&p);
    stg=1;
    dr=NMax;
     while (stg<=dr)
    {
        mijloc=(stg+dr)/2;
        if(zerouri(mijloc)<p)
            stg=mijloc+1;
        else
             if(zerouri(mijloc)>=p)
            {
                if(zerouri(mijloc)==p)
                    copie=mijloc;
                dr=mijloc-1;
            }
    }
        printf("%d",copie);


    return 0;
}