#include <cstdio>
int main (){
    freopen ("fact.in","r",stdin);
    freopen ("fact.out","w",stdout);
    int p,l1,l2,m,nr,s,n;
    scanf ("%d",&p);
    l1=1;
    l2=5*p;
    while (l1<=l2){
        m=(l1+l2)/2;
        nr=5;
        s=0;
        while (nr<=m && s<=p){
            s=s+m/nr;
            nr*=5;
        }
        if (s>=p){
            l2=m-1;
            n=m;
        }
        else
            l1=m+1;
    }
    if (p==0)
        n=1;
    printf ("%d",n);
    return 0;
}