#include <iostream>
#include <stdio.h>
using namespace std;

int main()
{
    FILE *fin, *fout;
    fin=fopen("fact.in", "r");
    fout=fopen("fact.out", "w");
    int d,p,n,e,cnt,cn;
    fscanf(fin, "%d", &p);
    cnt=0;
    n=0;
    while(cnt<p)
    {
        n++;
        cn=n;
        e=0;
        while(cn%5==0)
        {
            cn=cn/5;
            e++;
        }
        cnt=cnt+e;
    }
    if(n==0)
        n++;
    fprintf(fout, "%d", n);
    return 0;
}