#include <iostream>
#include <algorithm>
#include <cstdio>
#include <fstream>
using namespace std;
FILE*f=fopen("fact.in","r");
FILE*g=fopen("fact.out","w");
int main()
{
    int p,i;
    fscanf(f,"%d",&p);
    int f2=p,f5=p;
    for(p?i=1:i=2 ;f5;++i)
    {
        if(!(i%5))
        {
            int c=i;
            while(!(c%5))
            {
                --f5;
                c/=5;
            }
        }
    }
    fprintf(g,"%d\n",i-1);
    return 0;
}