#include <stdio.h>
#include <stdlib.h>
long p, n, k, s, ok;
int main()
{
    FILE *f, *g;
    f=fopen("fact.in", "r");
    g=fopen("fact.out", "w");
    fscanf(f, "%ld", &p);
    k=5;
    if (p==0){fprintf(g,"1"); return 0;}
    for(n=10;n<=100000000;n+=5)
    {
        while(n/k>0)
        {
            s=s +n/k;
            k=k*k;
        }
        if(s==p)
        {
        fprintf(g, "%ld", n);
        break;
        ok=1;}
        else{ k=5; s=0;}
    }
    if(ok!=1){fprintf(g, "-1");}
    fclose(f);
    fclose(g);


    return 0;
}