#include <fstream>
#define NMAX 1000000000 /// 10^9
using namespace std;
int nrz(int x) {
int sol;
sol = 0;
while (x) {
sol += x / 5;
x /= 5;
}
return sol;
}
int cautbin(int p) {
int st, dr, z, sol, mij;
st = 1;
dr = 1000000000;
while (st <= dr) {
mij = (st + dr) / 2;
z = nrz(mij);
if (z >= p) {
sol = mij;
dr = mij - 1;
}
else
st = mij + 1;
}
return sol;
}
int main() {
FILE *fin, *fout;
int p;
fin = fopen("factorial.in", "r");
fscanf(fin, "%d", &p);
fout = fopen("factorial.out", "w");
fprintf(fout, "%d", cautbin(p));
fclose( fout );
return 0;
}