#include<stdio.h>

	int putere(int n)
	{
		int k=0;
		while(n%5==0)
		{
			k++;
			n=n/5;
		}
		
		return k;
	}



	int main()
	{
		FILE *f, *g;
		int p,i=1,k=0;
		
		f=fopen("fact.in", "r");
		g=fopen("fact.out", "w");
		
		fscanf(f, "%d", &p);
		
		if(p==0)
		{
			fprintf(g, "1");
		}
		else
		{
			while(k<p)
			{
				k=k+putere(i);
				i++;
			}
			if(k!=p) fprintf(g, "-1");
		
			else
			{
				fprintf(g, "%d", i-1);
			}
		}
		
		
		
		return 0;
	}