#include<stdio.h>




int calc(int n)
{int nr=0;

    while(n%5==0)
	{
     n/=5;
	 nr++;
	}

 return nr;
}



int main()
{
	long p,i,s=0;
	FILE *f;

    f=fopen("fact.in","r");
	
	fscanf(f,"%li",&p);
	
    

    for(i=1;i<999999999;i++)
	{
      if(s==p || s>p) break;
	  else
		  s+=calc(i);
	}

    f=fopen("fact.out","w");
    if(s==p) fprintf(f,"%li",i-1);
	else fprintf(f,"%s","-1");

  
	



	return 0;
}