#include <cstdio>

using namespace std;

long p,n,i,p2,pp2,pp5,p5;
int main()
{FILE *f1 = fopen("fact.in","r");
FILE *f2 = fopen("fact.out","w");

fscanf(f1,"%ld",&p);
p5=0;p2=0;n=1;
while (p5<p || p2<p)
{pp5=0;pp2=0;i=n;
while (i%2==0) {i=i/2;pp2++;}
while (i%5==0) {i=i/5;pp5++;}
p2+=pp2;
p5+=pp5;n++;
}
if (p==0) fprintf(f2,"1");
else fprintf(f2,"%ld",n-1);
fclose(f1);fclose(f2);
    return 0;
}