#include <cstdio>

using namespace std;

int f(int a)
{
    int s=0,x=5;
    while(x<=a)
    {
        s=s+a/x;
        x = x*5;
    }
return s;
}

int main()
{
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
    int st=0,x,mij,dr=2000000000,p,n;
    scanf("%d",&p);

    while(st<=dr)
    {
         mij=(st+dr)/2;
         if(f(mij)>p)
         {
             dr=mij-1;
         }
         if(f(mij)<p)
         {
             st=mij+1;
         }
         if(f(mij)==p)
            n=mij,dr=mij-1;
    }
    printf("%d",n);
    return 0;
}