const input = [
  '10000'
];

const print = this.print || console.log;
const gets = this.gets || ((arr, index) => () => arr[index++])(input, 0);

let n = +gets();
let factorial = BigInt(1);

for (let i = 1; i <= n; i++) {
  factorial *= BigInt(i);
}

let trailingZeroesCount = 0;

let factorailStr = String(factorial);
for (let i = factorailStr.length - 1; i >= 0; i--) {
  if (factorailStr[i] !== '0') {
    break;
  }

  trailingZeroesCount++;
}

print(trailingZeroesCount);