#include <stdio.h>
long n,max;
void caut(long i, long j)
{
 if (i<=j) {
            long p,x=0,m=(i+j)/2;
            int q=1;
            p=5;
            while (q<12 && p<=m) {x+=m/p; p*=5;}
            if (x==n && (m<max || max==-1)) {max=m; caut(i,m-1);}
                    else if (x>n) caut(i,m-1);
                                    else caut(m+1,j);
            }

}

int main() {
FILE *f,*g;
f=fopen("fact.in","r");
g=fopen("fact.out","w");
fscanf(f,"%ld",&n);
max=-1;
if (n==0) fprintf(g,"0");
        else {
        caut (1,n*5);
        fprintf(g,"%ld",max);
        }
fclose(g);

return 0;
}