#include <cstdio>

#include <cstring>

using namespace std;

typedef long long ll;

const int N = 5e5 + ;

const ll inf = 1LL << ;

int n, d, dis[N], q[N];

ll cur, val[N], f[N];

template <typename T>

inline void read(T &X) {

    X = ; char ch = ; T op = ;

    for(; ch > '' || ch < ''; ch = getchar())

        if(ch == '-') op = -;

    for(; ch >= '' && ch <= ''; ch = getchar())

        X = (X << ) + (X << ) + ch - ;

    X *= op;

}

template <typename T>

inline void chkMax(T &x, T y) {

    if(y > x) x = y;

}

template <typename T>

inline int max(T x, T y) {

    return x > y ? x : y;

}

inline bool chk(int mid) {

    int st = max(, d - mid), ed = d + mid, l = , r = ;

    memset(f, 0LL, sizeof(f));

    for(int j = , i = ; i <= n; i++) {

        for(; j < i && dis[j] <= dis[i] - st; j++) {

            for(; l <= r && f[q[r]] < f[j]; --r);

            q[++r] = j;

        }

        for(; l <= r && dis[q[l]] < dis[i] - ed; ++l);

        ll mx = f[q[l]];

        if(l > r) mx = -inf;

        f[i] = mx + val[i];        

        if(f[i] >= cur) return ;

    }

    return ;

}    

/*inline bool chk(int mid) {

    int st = max(1, d - mid), ed = d + mid;

    memset(f, 0, sizeof(f));

    for(int i = 1; i <= n; i++) {

        int res = -inf;

        for(int j = 0; j < i; j++)

            if(dis[j] >= dis[i] - ed && dis[j] <= dis[i] - st)

                chkMax(res, f[j]);

        f[i] = res + val[i];

        if(f[i] >= cur) return 1;

    }

    return 0;

}   */

int main() {

    read(n), read(d), read(cur);

    int mn = ; ll sum = ;

    for(int i = ; i <= n; i++) {

        read(dis[i]), read(val[i]);

        chkMax(mn, dis[i]);

        if(val[i] > ) sum += val[i];

    }

    if(sum < cur) return puts("-1"), ;

    int ln = , rn = mn, mid, res = -;

    for(; ln <= rn; ) {

        mid = (ln + rn) / ;

        if(chk(mid)) rn = mid - , res = mid;

        else ln = mid + ;

    }   

    printf("%d\n", res);

    return ;

}