#include <stdio.h>
unsigned long p;

//calculeaza cate zerouri are la final x!
unsigned long zerouri(int x)
{
    unsigned long i=5, s=0;
    while (floor(x/i)>0)
    {
          s+=floor(x/i);
          i*=5;
    }
    return s;
}


unsigned long det(unsigned long p)
{
     unsigned long i=1, zero;
     //printf("intru\n");
     //printf("p=%lu\n", p);
     zero=zerouri(i);
     //printf("zero=%lu\n", zero);
     while (zero<p)
     {
         //printf("zero=%lu\n", zero);
         i++;
         zero=zerouri(i);
     }
     return i;
}


int main()
{
    FILE *f, *g;
    f=fopen("fact.in", "r");
    fscanf(f, "%lu", &p);
    g=fopen("fact.out", "w");    
    fprintf(g, "%lu\n", det(p));
    //getchar();
    return 0;
}