#include<stdio.h>
int main()
{
unsigned int p=0, p2=0, p5=0, n=1;

FILE *f=NULL;
f=fopen("fact.in","r");
fscanf(f,"%d\n",&p);
fclose(f);

n=0;
printf("Toate bune si frumoase...\np=%d\n",p);

while (p5<p){
n++;
p2=p2+((n%2)?0:1);
p5=p5+((n%5)?0:1);
}

printf("p2=%d, iar p5=%d\nn=%d", p2, p5, n);
f=fopen("fact.out","w");
if ((p2==p) && (p2==p5))
fprintf(f, "%d", n);
else
fprintf(f,"-1");
fclose(f);
return 0;
}