let input = require('fs').readFileSync('/dev/stdin', 'utf8');
const COUNT = Array(3);
[...'tre'].forEach((v, i) => {
  COUNT[i] = [...input].filter(x => x == v).length;
});
let TMP = 0;
while (1) {
  COUNT[0]--;
  COUNT[1]--;
  COUNT[2] -= 2;
  if (!COUNT.every(v => v >= 0)) {
    console.log(TMP);
    return;
  }
  TMP++;
}