#include<iostream>
using namespace std;
#include<stdio.h>
#include<stdlib.h>
FILE *f,*g;
long long a,b=1000000000,p,mij,u;
int desc(int z)
{long long d=0;
    while(z/5)
    {
      d=d+z/5;
        z=z/5;
    }
    return d;
}
int caut(int x,int y)
{
    if(x<y)
    {
        mij=(x+y)/2;

        u=desc(mij);
        if(u>p)
        caut(x,mij-1);
        else
        if(u<p)
            caut(mij+1,y);
            else
        if(u==p)
           {
               while(mij%5)
                mij--;
               fprintf(g,"%lld",mij);
               exit(EXIT_SUCCESS);
           }
    }
}
int main()
{
    f=fopen("fact.in","r");
    g=fopen("fact.out","w");
    fscanf(f,"%lld",&p);
    if(p==0)
        fprintf(g,"1");
    else
    caut(0,b);

}