#include<stdio.h>

int main()
{
    FILE *in, *out;
    int N=0, P, c5=0, i;
    in=fopen("fact.in", "r");
    out=fopen("fact.out", "w");
    
    fscanf(in, "%d", &P);
    
    while (c5<P)
        {   
            N++;
            i=N;
            while (i%5==0)
            {
                i/=5; 
                if (c5<P) c5++;
                else break;
            }
        }
    if(!c5) fprintf(out, "%d", -1);
    else fprintf(out, "%d", N);
    return 0;
}