const rl = require("readline").createInterface({ input: process.stdin });
var iter = rl[Symbol.asyncIterator]();
const readline = async () => (await iter.next()).value;
void (async function () {
const n = Number(await readline());
const steps = [];
for (let i = 0; i < 2 * n; i++) {
steps.push(await readline());
}
let queue = [];
let deleteVal = 1;
let ans = 0;
for (let i = 0; i < steps.length; i++) {
const step = steps[i];
if (step.startsWith("remove")) {
if (queue[0] == deleteVal) {
queue.shift();
} else {
queue.sort((a, b) => a - b);
ans++;
queue.shift();
}
} else {
const [str, _, num] = step.split(" ");
if (str == "head") queue.unshift(Number(num));
else queue.push(Number(num));
}
}
console.log(ans);
})();