#include<stdio.h>
#include<conio.h>
//0 2 4 10
int main()
{
    FILE *in, *out;
    int N=1, i=1, P, c2=0, c5=0, nrz=0;
    in=fopen("fact.in", "r");
    out=fopen("fact.out", "w");
    
    fscanf(in, "%d", &P);
    
    while (nrz<P)
        {
            i=N;
            while (i%2==0) 
            {
                i/=2; c2++;
            }
            while (i%5==0)
            {
                i/=5; c5++;
            }
            if (c2<c5) nrz=c2;
            else nrz=c5;
            N++;
        }
    if(!nrz) fprintf(out, "%d", -1);
    else fprintf(out, "%d", N-1);
 getch();
    return 0;
}