#include <iostream>
#include <cstdio>
#include <string>
#include <cstring>
#include <cstdlib>
#include <map>
#include <unordered_map>
#include <queue>
#include <vector>
#include <list>
#include <algorithm>
#include <cmath>
#include <set>
#include <unordered_set>
#include <numeric>

using namespace std;
typedef unsigned long long ull;
typedef long long ll;
#define REP(i,n) for(int (i) = 0; (i) < (n); ++(i))
#define FOR(i,a,b) for(int (i) = a; (i) < (b); ++(i))

int t[1010];
ll b[1010];
ll f[1010][1010];

int main ()
{
    int n, k;
    ll p;
    cin >> n >> p >> k;
    REP(i,n) {
        cin >> t[i] >> b[i];
    }
    REP(i, n) {
        f[i][0] = p;
        if (i == 0) {
            if (t[0] == 1)
                f[i][1] = p + b[0];
            else
                f[i][1] = p * 2;
            continue;
        }
        FOR(j, 1, k+1) {
            f[i][j] = f[i-1][j];
            if (f[i-1][j-1] > 0) {
                if (t[i] == 1)
                    f[i][j] = max(f[i][j], f[i-1][j-1] + b[i]);
                else
                    f[i][j] = max(f[i][j], f[i-1][j-1] * 2);
            } else continue;
            f[i][j] = min(f[i][j], (ll)(1e18) + 1);
            //cout << i << " " << j << " " << f[i][j] << endl;
        }
    }
    ll ans = f[n-1][k];
    if (ans > 1e18) ans = -1;
    cout << ans << endl;
}