#include <cstdio>

int putere(int a, int b)
{
    int out = 1;
    while (a%b==0)
    {
        out++;
        a=a/b;
    }
    return out;
}
int main()
{
    FILE *f = fopen("fact.in", "r");
    FILE *fout = fopen("fact.out", "w");

    int P=0, out=0, corect=0;
    fscanf(f,"%d", &P);
    if (P==0) fprintf(fout, "%d", 1); 
    else {
        for (int i=1;i<=P && corect<P;i++)
        {
            int tmp = putere(i,5);
            out += 5;
            corect += tmp;
        }
    }
    if (corect==P) {
        fprintf(stdout, "%d", out);
    }
    else fprintf(fout, "%d", -1);

    
    return 0;
}