#include <stdio.h>
#include <math.h>
int main(){
	int p, N, five = 25, power = 2;
	FILE * f1;
	FILE * f2;
	f1 = fopen ("fact.in","r");
	f2 = fopen ("fact.out","w");
	fscanf (f1, "%d", &p);
	//scanf("%d",&p);
	if(p) { N = 0; }
	else { N = 1; }

    while(p > 0){
        N += 5;
        if(N == five){
            p -= power;
            power++;
            five *= 5;
        }
        else{ p--; }
    }
    if(!p){
        fprintf(f2,"%d\n", N);
    }
    else{
        fprintf(f2, "-1\n");
    }
    //printf("N final:%d\n", N);

	fflush(stdout);
	fclose(f1);
	fclose(f2);
    return 0;
}